Stock Plans - Share Repurchase Program (Details) - USD ($) $ / shares in Units, shares in Millions		3 Months Ended	6 Months Ended		84 Months Ended
	Jan. 31, 2018	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019	Dec. 31, 2018
Class of Stock [Line Items]
Common shares repurchased		$ 276,000,000	$ 701,000,000	$ 941,000,000
Common Stock | Prior to January 1, 2020
Class of Stock [Line Items]
Stock repurchase value						$ 13,700,000,000
Common shares repurchased					$ 16,500,000,000
Common Stock | Share Repurchase Program Amended January 31, 2018
Class of Stock [Line Items]
Stock repurchase value	$ 19,700,000,000
Increase in share repurchase value	$ 6,000,000,000.0
Stock repurchase expiration date	Dec. 31, 2020
Common shares repurchased			$ 700,000,000
Number of shares repurchased (in shares)			12.9
Average cost of shares repurchased (in dollars per share)			$ 54.25
Remaining share repurchase capacity			$ 2,500,000,000