Shareholders' Equity and Dividend Availability (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Apr. 30, 2017
Stockholders' Equity Note [Abstract]
Number of authorized shares (in shares)	1,755.0
Number of authorized shares, preferred shares (in shares)	5.0
Number of authorized shares, voting common stock (in shares)	1,745.0
Number of authorized shares, undesignated shares (in shares)	5.0
Additional share repurchase authorization			$ 5,000
Number of shares repurchased (in shares)	4.9
Cost of shares repurchased	$ 625
Average cost per share repurchased (in dollars per share)	$ 127.17
Remaining capacity under share repurchase authorization	$ 1,160
Cost of shares acquired to cover tax withholding costs and exercise costs	$ 47	$ 48