Disclosures About Fair Value Measurements (Company's Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Detail) - USD ($) $ in Millions | Jun. 30, 2017 | Dec. 31, 2016 |
Fair Value Of Derivatives Disclosure Information [Line Items] | | |
Derivative, Fair Value, Net | $ 225 | $ (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 | 145 | 59 |
Derivative Asset, Fair Value, Gross Liability | (10) | (55) |
Derivative Asset, Fair Value, Amount Not Offset Against Collateral | 135 | 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 | 94 | 0 |
Derivative Asset, Fair Value, Gross Liability | (4) | 0 |
Derivative Asset, Fair Value, Amount Not Offset Against Collateral | 90 | 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 | (10) | (137) |
Derivative Liability, Fair Value, Gross Asset | 10 | 55 |
Derivative Liability, Fair Value, Amount Not Offset Against Collateral | 0 | (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 | (4) | (96) |
Derivative Liability, Fair Value, Gross Asset | 4 | 0 |
Derivative Liability, Fair Value, Amount Not Offset Against Collateral | 0 | (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 | 225 | (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 | 145 | 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 | 94 | 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 | (10) | (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 | (4) | (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 |