Employment Benefit Plans AOCI (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2015	Dec. 31, 2014
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Future amortization of actuarial losses and prior service credits, Less than	$ 1
Defined Benefit Plan, Change in Accumulated Other Comprehensive Income Loss [Roll Forward]
Beginning balance	34	$ 427	$ (330)
Amortization of net loss	2	1	17
Amortization of prior service credits	(1)	(1)	0
Prior service credits	0	0	7
Actuarial (loss) gain	68	(392)	734
Settlements	(1)	(1)	(1)
Ending balance	102	34	427
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), before Tax [Abstract]
Net gain (loss)				$ 99	$ 29
Prior Service Credits				5	6
Settlements				(2)	(1)
Pre-tax amount recognized in AOCI at December 31,	34	427	(330)	102	34
After-tax amount recognized in AOCI at December 31,				63	21
Retiree Health and Welfare Benefits
Defined Benefit Plan Disclosure [Line Items]
Future amortization of prior service credits	1
Future amortization of actuarial loss, Less than	1
Defined Benefit Plan, Change in Accumulated Other Comprehensive Income Loss [Roll Forward]
Beginning balance	(34)	(20)	(60)
Amortization of net loss	2	1	5
Amortization of prior service credits	(2)	(2)	(1)
Prior service credits	0	0	7
Actuarial (loss) gain	13	(13)	29
Ending balance	(21)	(34)	(20)
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), before Tax [Abstract]
Net gain (loss)				(28)	(43)
Prior Service Credits				7	9
Settlements				0	0
Pre-tax amount recognized in AOCI at December 31,	$ (34)	$ (20)	$ (60)	(21)	(34)
After-tax amount recognized in AOCI at December 31,				$ (13)	$ (21)