Disclosures About Fair Value Measurements (Company's Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Detail) - USD ($) $ in Millions | Mar. 31, 2017 | Dec. 31, 2016 |
Fair Value Of Derivatives Disclosure Information [Line Items] | | |
Derivative, Fair Value, Net | $ 84 | $ (174) |
Commodity Derivative Price Swap Contracts [Member] | Derivative Asset Current [Member] | | |
Fair Value Of Derivatives Disclosure Information [Line Items] | | |
Derivative Asset, Fair Value, Gross Asset | 98 | 59 |
Derivative Asset, Fair Value, Gross Liability | (43) | (55) |
Derivative Asset, Fair Value, Amount Not Offset Against Collateral | 55 | 4 |
Commodity Derivative Price Swap Contracts [Member] | Derivative Asset Noncurrent [Member] | | |
Fair Value Of Derivatives Disclosure Information [Line Items] | | |
Derivative Asset, Fair Value, Gross Asset | 60 | 0 |
Derivative Asset, Fair Value, Gross Liability | (18) | 0 |
Derivative Asset, Fair Value, Amount Not Offset Against Collateral | 42 | 0 |
Commodity Derivative Price Swap Contracts [Member] | Derivative Liability Current [Member] | | |
Fair Value Of Derivatives Disclosure Information [Line Items] | | |
Derivative Liability, Fair Value, Gross Liability | (53) | (137) |
Derivative Liability, Fair Value, Gross Asset | 43 | 55 |
Derivative Liability, Fair Value, Amount Not Offset Against Collateral | (10) | (82) |
Commodity Derivative Price Swap Contracts [Member] | Derivative Liability Noncurrent [Member] | | |
Fair Value Of Derivatives Disclosure Information [Line Items] | | |
Derivative Liability, Fair Value, Gross Liability | (21) | (96) |
Derivative Liability, Fair Value, Gross Asset | 18 | 0 |
Derivative Liability, Fair Value, Amount Not Offset Against Collateral | (3) | (96) |
Fair Value Inputs Level 1 [Member] | | |
Fair Value Of Derivatives Disclosure Information [Line Items] | | |
Derivative, Fair Value, Net | 0 | 0 |
Fair Value Inputs Level 1 [Member] | Commodity Derivative Price Swap Contracts [Member] | Derivative Asset Current [Member] | | |
Fair Value Of Derivatives Disclosure Information [Line Items] | | |
Derivative Asset, Fair Value, Gross Asset | 0 | 0 |
Fair Value Inputs Level 1 [Member] | Commodity Derivative Price Swap Contracts [Member] | Derivative Asset Noncurrent [Member] | | |
Fair Value Of Derivatives Disclosure Information [Line Items] | | |
Derivative Asset, Fair Value, Gross Asset | 0 | 0 |
Fair Value Inputs Level 1 [Member] | Commodity Derivative Price Swap Contracts [Member] | Derivative Liability Current [Member] | | |
Fair Value Of Derivatives Disclosure Information [Line Items] | | |
Derivative Liability, Fair Value, Gross Liability | 0 | 0 |
Fair Value Inputs Level 1 [Member] | Commodity Derivative Price Swap Contracts [Member] | Derivative Liability Noncurrent [Member] | | |
Fair Value Of Derivatives Disclosure Information [Line Items] | | |
Derivative Liability, Fair Value, Gross Liability | 0 | 0 |
Fair Value Inputs Level 2 [Member] | | |
Fair Value Of Derivatives Disclosure Information [Line Items] | | |
Derivative, Fair Value, Net | 84 | (174) |
Fair Value Inputs Level 2 [Member] | Commodity Derivative Price Swap Contracts [Member] | Derivative Asset Current [Member] | | |
Fair Value Of Derivatives Disclosure Information [Line Items] | | |
Derivative Asset, Fair Value, Gross Asset | 98 | 59 |
Fair Value Inputs Level 2 [Member] | Commodity Derivative Price Swap Contracts [Member] | Derivative Asset Noncurrent [Member] | | |
Fair Value Of Derivatives Disclosure Information [Line Items] | | |
Derivative Asset, Fair Value, Gross Asset | 60 | 0 |
Fair Value Inputs Level 2 [Member] | Commodity Derivative Price Swap Contracts [Member] | Derivative Liability Current [Member] | | |
Fair Value Of Derivatives Disclosure Information [Line Items] | | |
Derivative Liability, Fair Value, Gross Liability | (53) | (137) |
Fair Value Inputs Level 2 [Member] | Commodity Derivative Price Swap Contracts [Member] | Derivative Liability Noncurrent [Member] | | |
Fair Value Of Derivatives Disclosure Information [Line Items] | | |
Derivative Liability, Fair Value, Gross Liability | (21) | (96) |
Fair Value Inputs Level 3 [Member] | | |
Fair Value Of Derivatives Disclosure Information [Line Items] | | |
Derivative, Fair Value, Net | 0 | 0 |
Fair Value Inputs Level 3 [Member] | Commodity Derivative Price Swap Contracts [Member] | Derivative Asset Current [Member] | | |
Fair Value Of Derivatives Disclosure Information [Line Items] | | |
Derivative Asset, Fair Value, Gross Asset | 0 | 0 |
Fair Value Inputs Level 3 [Member] | Commodity Derivative Price Swap Contracts [Member] | Derivative Asset Noncurrent [Member] | | |
Fair Value Of Derivatives Disclosure Information [Line Items] | | |
Derivative Asset, Fair Value, Gross Asset | 0 | 0 |
Fair Value Inputs Level 3 [Member] | Commodity Derivative Price Swap Contracts [Member] | Derivative Liability Current [Member] | | |
Fair Value Of Derivatives Disclosure Information [Line Items] | | |
Derivative Liability, Fair Value, Gross Liability | 0 | 0 |
Fair Value Inputs Level 3 [Member] | Commodity Derivative Price Swap Contracts [Member] | Derivative Liability Noncurrent [Member] | | |
Fair Value Of Derivatives Disclosure Information [Line Items] | | |
Derivative Liability, Fair Value, Gross Liability | $ 0 | $ 0 |