Accumulated Other Comprehensive Income Reclassifications out of AOCI (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before Tax	[1]	$ 2	$ 2
Tax (expense) / benefit	[1]	0	(1)
Net of Tax	[1],[2]	2	1
Amortization of prior service costs/ credits [Member] | Accumulated Defined Benefit Plans Adjustment, Net Prior Service Attributable to Parent [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before Tax	[1],[3]	2	3
Amortization of Actuarial Gains/ Losses [Member] | Accumulated Defined Benefit Plans Adjustment, Net Prior Service Attributable to Parent [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before Tax	[1],[3]	$ 0	$ (1)

[1] Amounts in parenthesis indicate debits to the income statement.

[2] Amounts are net of tax. See Note 13 to the Consolidated Financial Statements for additional details.

[3] This accumulated other comprehensive income component is included in the computation of net periodic pension and retiree health and welfare cost (see Note 13 to the Consolidated Financial Statements for additional details).