Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Income Tax Disclosure [Abstract]
Provision for income taxes before discrete items	$ (128)	$ (111)	$ (240)	$ (245)
Tax benefit from transfer of assets	0	0	768	0
Provision for gain on sale of assets	0	0	(163)	0
Other discrete items	9	(2)	12	(3)
(Provision) benefit for income taxes	$ (119)	$ (113)	$ 377	$ (248)
Effective income tax rate	20.80%	21.20%	(22.50%)	20.80%
Deferred tax asset, period of expected benefit			25 years
Decrease to reserve for uncertain tax positions			$ 146