Income Taxes - Unrecognized Tax Benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Reconciliation of Unrecognized Tax Benefits [Roll Forward]
Balance at beginning of year	$ 1,442	$ 1,409	$ 802
Additions due to acquisitions			31
Reductions due to acquisitions		(5)
Additions for tax positions of current year	53	48	565
Additions for tax positions of prior years	69	82	51
Reductions for tax positions of prior years	(7)	0	0
Closure of tax years		(5)
Settlements	(5)	(87)	(40)
Balance at end of year	1,552	1,442	1,409
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued	67	59
Federal and State [Member]
Reconciliation of Unrecognized Tax Benefits [Roll Forward]
Unrecognized Tax Benefits, Period Increase (Decrease)	45	45
Tax Cuts and Jobs Act of 2017, Uncertain Tax Positions [Member]
Reconciliation of Unrecognized Tax Benefits [Roll Forward]
Additions for tax positions of current year			511
Foreign Tax Positions [Member]
Reconciliation of Unrecognized Tax Benefits [Roll Forward]
Additions for tax positions of current year			54
Unrecognized Tax Benefits, Period Increase (Decrease)	$ 70	$ 85
Foreign Exchange Loss On Refinancing Long-term Intercompany Debt [Member]
Reconciliation of Unrecognized Tax Benefits [Roll Forward]
Additions for tax positions of prior years			$ 43