Common Stock (Details) - USD ($) shares in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Nov. 30, 2019
Equity, Class of Treasury Stock [Line Items]
Consideration for purchase of common stock	$ 485,000,000	$ 675,000,000	$ 900,000,000
Shares issued in period (in shares)	4.6	3.3
Common stock
Equity, Class of Treasury Stock [Line Items]
Common stock repurchased (in shares)	4.8	8.2
Stock repurchase program, authorized amount				$ 2,500,000,000
Stock repurchase program, remaining authorized repurchase amount	$ 2,400,000,000