Employment Benefit Plans AOCI (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2016	Dec. 31, 2015
Pension Plan [Member]
Defined Benefit Plan, Change in Accumulated Other Comprehensive Income Loss [Roll Forward]
Beginning balance	$ 102	$ 34	$ 427
Amortization of net loss	1	2	1
Amortization of prior service credits	(1)	(1)	(1)
Actuarial (loss) gain	106	68	(392)
Settlements	(1)	(1)	(1)
Ending balance	207	102	34
Future amortization of prior service credits	1
Future amortization of actuarial loss, Less than	1
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), before Tax [Abstract]
Net gain (loss)				$ 206	$ 99
Prior Service Credits				4	5
Settlements				(3)	(2)
Pre-tax amount recognized in AOCI at December 31,	102	34	427	207	102
After-tax amount recognized in AOCI at December 31,				128	63
Retiree Health and Welfare Benefits [Member]
Defined Benefit Plan, Change in Accumulated Other Comprehensive Income Loss [Roll Forward]
Beginning balance	(21)	(34)	(20)
Amortization of net loss	1	2	1
Amortization of prior service credits	(2)	(2)	(2)
Actuarial (loss) gain	13	13	(13)
Ending balance	(9)	(21)	(34)
Future amortization of prior service credits	1
Future amortization of actuarial loss, Less than	1
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), before Tax [Abstract]
Net gain (loss)				(14)	(28)
Prior Service Credits				5	7
Settlements				0	0
Pre-tax amount recognized in AOCI at December 31,	$ (21)	$ (34)	$ (20)	(9)	(21)
After-tax amount recognized in AOCI at December 31,				$ (6)	$ (13)