Common Stock (Details) - USD ($) shares in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Nov. 30, 2016
Equity, Class of Treasury Stock [Line Items]
Payments for repurchase of common stock	$ 675,000,000	$ 900,000,000	$ 800,000,000
Shares issued in period	3.3	5.8
Common Stock
Equity, Class of Treasury Stock [Line Items]
Common stock repurchased (in shares)	8.2	11.5
Stock repurchase program, authorized amount				$ 2,500,000,000.0
Stock repurchase program, remaining authorized repurchase amount	$ 866,000,000