Retirement and Employee Benefit Plans (Fair Value Measurement of Pension Plan Assets) (Details) - Pension Benefits [Member] - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 91	$ 101	$ 81
Quoted Prices in Active Markets for Identical Assets, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	72	83
Excluding Net Assets Value [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	72	83
Net Asset Value [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	19	18
Equity Securities [Member] | U.S. Large Cap Growth Equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	5	7
Equity Securities [Member] | U.S. Large Cap Growth Equity [Member] | Quoted Prices in Active Markets for Identical Assets, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	5	7
Equity Securities [Member] | U.S. Large Cap Value Equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	5	8
Equity Securities [Member] | U.S. Large Cap Value Equity [Member] | Quoted Prices in Active Markets for Identical Assets, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	5	8
Equity Securities [Member] | U.S. Large Cap Core Equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		18
Equity Securities [Member] | U.S. Large Cap Core Equity [Member] | Net Asset Value [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	12
Equity Securities [Member] | U.S. Small Cap Equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2	3
Equity Securities [Member] | U.S. Small Cap Equity [Member] | Quoted Prices in Active Markets for Identical Assets, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2	3
Equity Securities [Member] | Non-U.S. Equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	20	30
Equity Securities [Member] | Non-U.S. Equity [Member] | Quoted Prices in Active Markets for Identical Assets, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	20	30
Equity Securities [Member] | Emerging Markets Equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	3	5
Equity Securities [Member] | Emerging Markets Equity [Member] | Quoted Prices in Active Markets for Identical Assets, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	3	5
Fixed Income [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	14	27
Fixed Income [Member] | Quoted Prices in Active Markets for Identical Assets, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	14	27
Fixed Income [Member] | Net Asset Value [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	7
Cash and Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	23	3
Cash and Cash Equivalents [Member] | Quoted Prices in Active Markets for Identical Assets, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	23	$ 3
Fayetteville Shale [Member] | Cash and Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 21