Comprehensive Income (Loss) (Reclassification Out of AOCI) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income before income taxes		$ (623)	$ (361)	$ 163
Tax impact		250	165	(30)
Net income (loss)		(373)	(196)	133
Pension Benefits [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Actuarial gains (losses)	[1],[2]	(40)	(29)	(20)
Income before income taxes	[1],[2]	(40)	(29)	(20)
Tax impact	[1],[2]	15	11	7
Net income (loss)	[1],[2]	(25)	(18)	(13)
Postretirement Costs [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Prior service (cost) credit recognized during year	[1],[2]	9	5	4
Actuarial gains (losses)	[1],[2]	(1)	(8)	(3)
Income before income taxes	[1],[2]	8	(3)	1
Tax impact	[1],[2]	(3)	1
Net income (loss)	[1],[2]	$ 5	$ (2)	$ 1

[1] Amounts in parentheses indicate losses.

[2] These accumulated other comprehensive loss components are included in the computation of net periodic pension and OPEB costs (see Note 17 - Retirement Plans for additional details).