Income Taxes - Reconciliation of Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Taxes [Line Items]
Federal statutory tax rate		21.00%	35.00%	35.00%
Reconciliation of Statutory to Effective Tax (Benefit) Expense
U.S. federal income tax expense at the statutory rate of 21% (35% for 2017 and 2016)		$ 212	$ 307	$ 422
Adjustment for foreign income taxed at different rates		30	(55)	(51)
U.S. charges (benefits) related to foreign tax credits and R&D		20	(23)	(163)
Net establishment (resolution) of uncertain tax positions		18	(6)	3
Provision for undistributed foreign earnings, net	$ 171	(9)	(162)	0
Transition tax		8	77	0
Net foreign losses (income) with no tax due to valuation allowances		7	(7)	8
State income taxes, net of U.S. federal benefit		(1)	9	16
Domestic production activities deduction		(1)	(16)	(3)
Other		(1)	(6)	8
Deferred tax impact of enacted tax rate and law changes		0	389	(2)
United States and Foreign Taxes		303	513	(77)
Domestic Tax Authority
Reconciliation of Statutory to Effective Tax (Benefit) Expense
Net establishment (release) of valuation allowances		25	5	39
Foreign Tax Authority
Reconciliation of Statutory to Effective Tax (Benefit) Expense
Net establishment (release) of valuation allowances		$ (5)	$ 1	$ (354)