Employment Benefit Plans AOCI (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Pension Plan [Member]
Defined Benefit Plan, Change in Accumulated Other Comprehensive Income Loss [Roll Forward]
Amortization of net loss	$ 1	$ 0	$ 1
Amortization of prior service credits	(1)	0	(1)
Actuarial (loss) gain	(188)	164	106
Settlements	(1)	0	(1)
Ending balance	182	371	207	$ 102
Expected Amortization of Prior Service Credit, Next Fiscal Year	1
Expected Amortization of Loss, Next Fiscal Year	2
Defined Benefit Plan, Accumulated Other Comprehensive (Income) Loss, before Tax [Abstract]
Net gain (loss)	183	370
Prior Service Credits	3	4
Settlements	(4)	(3)
Pre-tax amount recognized in AOCI at December 31,	(182)	(371)	(207)	(102)
After-tax amount recognized in AOCI at December 31,	108	251
Retiree Health and Welfare Benefits [Member]
Defined Benefit Plan, Change in Accumulated Other Comprehensive Income Loss [Roll Forward]
Amortization of net loss	0	0	1
Amortization of prior service credits	(2)	(2)	(2)
Actuarial (loss) gain	22	(14)	13
Prior Service credit	0	1	0
Ending balance	(4)	(24)	(9)	(21)
Expected Amortization of Prior Service Credit, Next Fiscal Year	1
Defined Benefit Plan, Accumulated Other Comprehensive (Income) Loss, before Tax [Abstract]
Net gain (loss)	(6)	(28)
Prior Service Credits	2	4
Settlements	0	0
Pre-tax amount recognized in AOCI at December 31,	4	24	$ 9	$ 21
After-tax amount recognized in AOCI at December 31,	$ (2)	$ (17)