Common Stock (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Nov. 30, 2019
Equity, Class of Treasury Stock [Line Items]
Consideration for purchase of common stock	$ 0	$ 485,000,000	$ 675,000,000
Shares issued in period (in shares)	4,100,000	4,600,000
Common stock
Equity, Class of Treasury Stock [Line Items]
Common stock repurchased (in shares)	0	4,800,000
Stock repurchase program, authorized amount				$ 2,500,000,000
Stock repurchase program, remaining authorized repurchase amount	$ 2,400,000,000