Accumulated Other Comprehensive Income Reclassifications out of AOCI (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2018		Dec. 31, 2017
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before Tax	[1]	$ (23)		$ 2
Tax (expense) / benefit	[1]	(1)		0
Net of Tax	[2]	(25)		2	[1]
Accumulated Other Comprehensive Income (Loss) [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net of Tax		(24)	[1]	2
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]	3		2
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]	(1)		0
Accounting Standards Update 2016-01 [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before Tax		1		0
Accounting Standards Update 2018-02 [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before Tax		$ (26)		$ 0

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

[2] Amounts are net of tax. See Note 14 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 14 to the Consolidated Financial Statements for additional details).