Stock Compensation - Effects on Cash Flows (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Payment Arrangement [Abstract]
Proceeds from common stock transactions	[1]	$ 470	$ 539	$ 373
Tax benefit realized from stock compensation		195	224	179
Reduction to deferred tax asset		(44)	(49)	(43)
Excess tax benefit for stock compensation		151	175	136
Taxes paid for employee shares withheld		$ 53	$ 52	$ 60

[1] Net of taxes paid for employee shares withheld of $53 million, $52 million and $60 million in 2020, 2019 and 2018, respectively.