Accumulated Other Comprehensive Income Reclassifications out of AOCI (Details) - Reclassification out of Accumulated Other Comprehensive Income [Member] - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net of Tax		$ 1	$ 0
Pension and Retiree Health and Welfare Benefit Items [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Actuarial losses	[1],[2]	(1)	(4)
Prior service credits	[1],[2]	3	3
Total before Tax	[1]	2	(1)
Tax (expense) / benefit	[1]	(1)	1
Net of Tax	[1],[3]	$ 1	$ 0

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

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

[3] Amounts are net of tax. See Note 13 for additional details.