Fair Value
 
The fair values of our financial instruments are separated into three broad levels (Levels 1, 2 and 3) based on our assessment of the availability of observable market data and the significance of non-observable data used to determine fair value. Each fair value measurement must be assigned to a level corresponding to the lowest level input that is significant to the fair value measurement in its entirety.

The three broad levels of inputs defined by the fair value hierarchy are as follows:
Level 1 Inputs—quoted prices (unadjusted) in active markets for identical assets or liabilities that the reporting entity has the ability to access at the measurement date;
Level 2 Inputs—inputs other than quoted prices included within Level 1 that are observable for the asset or liability, either directly or indirectly. If the asset or liability has a specified (contractual) term, a Level 2 input must be observable for substantially the full term of the asset or liability; and
Level 3 Inputs—unobservable inputs for the asset or liability. These unobservable inputs reflect the entity’s own assumptions about the assumptions that market participants would use in pricing the asset or liability, and are developed based on the best information available in the circumstances (which might include the reporting entity’s own data).

Fair Value of Derivative Contracts
 
The following two tables summarize the fair value measurements of our (i) energy commodity derivative contracts; (ii) interest rate swap agreements; and (iii) cross-currency swap agreements, based on the three levels established by the Codification (in millions). The tables also identify the impact of derivative contracts which we have elected to present on our accompanying consolidated balance sheets on a gross basis that are eligible for netting under master netting agreements. 
 
Balance sheet asset fair value measurements by level
 
 
 
 
 

Level 1
 

Level 2
 

Level 3
 
Gross amount
 
Contracts available for netting
 
Cash collateral held(b)
 
Net amount
As of December 31, 2018
 
 
 
 
 
 
 
 
 
 
 
 
 
Energy commodity derivative contracts(a)
$
28

 
$
193

 
$

 
$
221

 
$
(39
)
 
$
(25
)
 
$
157

Interest rate contracts
$

 
$
133

 
$

 
$
133

 
$
(7
)
 
$

 
$
126

Foreign currency contracts
$

 
$
197

 
$

 
$
197

 
$
(6
)
 
$

 
$
191

As of December 31, 2017
 

 
 

 
 

 
 
 
 
 
 
 
 
Energy commodity derivative contracts(a)
$
17

 
$
70

 
$

 
$
87

 
$
(42
)
 
$
(12
)
 
$
33

Interest rate contracts
$

 
$
205

 
$

 
$
205

 
$
(15
)
 
$

 
$
190

Foreign currency contracts
$

 
$
166

 
$

 
$
166

 
$
(6
)
 
$

 
$
160


 
Balance sheet liability
fair value measurements by level
 
 
 
 
 
Level 1
 
Level 2
 
Level 3
 
Gross amount
 
Contracts available for netting
 
Collateral posted(b)
 
Net amount
As of December 31, 2018
 
 
 
 
 
 
 
 
 
 
 
 
 
Energy commodity derivative contracts(a)
$
(11
)
 
$
(39
)
 
$

 
$
(50
)
 
$
39

 
$

 
$
(11
)
Interest rate contracts
$

 
$
(115
)
 
$

 
$
(115
)
 
$
7

 
$

 
$
(108
)
Foreign currency contracts
$

 
$
(6
)
 
$

 
$
(6
)
 
$
6

 
$

 
$

As of December 31, 2017
 
 
 
 
 
 
 
 
 
 
 
 
 
Energy commodity derivative contracts(a)
$
(3
)
 
$
(98
)
 
$

 
$
(101
)
 
$
42

 
$

 
$
(59
)
Interest rate contracts
$

 
$
(65
)
 
$

 
$
(65
)
 
$
15

 
$

 
$
(50
)
Foreign currency contracts
$

 
$
(6
)
 
$

 
$
(6
)
 
$
6

 
$

 
$

_______
(a)
Level 1 consists primarily of NYMEX natural gas futures.  Level 2 consists primarily of OTC WTI swaps and NGL swaps. 
(b)
Any cash collateral paid or received is reflected in this table, but only to the extent that it represents variation margins. Any amount associated with derivative prepayments or initial margins that are not influenced by the derivative asset or liability amounts or those that are determined solely on their volumetric notional amounts are excluded from this table.

Fair Value of Financial Instruments
 
The carrying value and estimated fair value of our outstanding debt balances is disclosed below (in millions): 
 
December 31, 2018
 
December 31, 2017
 
Carrying
value
 
Estimated
fair value
 
Carrying
value
 
Estimated
fair value
Total debt
$
37,324

 
$
37,469

 
$
37,843

 
$
40,050



We used Level 2 input values to measure the estimated fair value of our outstanding debt balance as of both December 31, 2018 and 2017.

Historical Timeline

Fiscal YearFiled
2018Feb 8, 2019Showing above
2017Feb 9, 2018
2016Feb 10, 2017
2015Feb 16, 2016

About Fair Value Disclosures

Fair value disclosures classify all assets and liabilities measured at fair value into a three-level hierarchy: Level 1 (quoted market prices), Level 2 (observable inputs like yield curves), and Level 3 (unobservable inputs requiring management estimates). The proportion of Level 3 assets directly reflects how much of the balance sheet depends on internal models rather than market evidence.

Key signals: a growing Level 3 balance relative to total fair-value assets increases valuation uncertainty and earnings volatility risk. Watch for transfers between levels — assets moving from Level 2 to Level 3 often signal deteriorating market liquidity. Unrealized gains and losses on Level 3 positions flow through earnings or other comprehensive income, so large swings deserve scrutiny. For financial institutions, examine the sensitivity disclosures that show how Level 3 valuations change under alternative assumptions. Compare the fair value of debt against its carrying amount to gauge hidden leverage.