Retirement and Employee Benefit Plans (Fair Value Measurement of Pension Plan Assets) (Details) - Pension Benefits [Member] - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 101	$ 81	$ 108
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	83	67
Excluding Net Assets Value [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	83	67
Net Asset Value [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	18	14
Equity Securities [Member] | U.S. Large Cap Growth Equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	7	6
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	7	6
Equity Securities [Member] | U.S. Large Cap Value Equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	8	6
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	8	6
Equity Securities [Member] | U.S. Large Cap Core Equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		14
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	18
Equity Securities [Member] | U.S. Small Cap Equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	3	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	3	3
Equity Securities [Member] | Non-U.S. Equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	30	23
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	30	23
Equity Securities [Member] | Emerging Markets Equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	5	4
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	5	4
Fixed Income [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	27	21
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	27	21
Cash [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	3	4
Cash [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 3	$ 4