Common Stock (Details) - USD ($) shares in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Nov. 30, 2016
Equity, Class of Treasury Stock [Line Items]
Payments for repurchase of common stock	$ 0	$ 250,000,000
Stock-based compensation, shares issued during period	3.2	2.3
Common Stock
Equity, Class of Treasury Stock [Line Items]
Payments for repurchase of common stock	$ 0	$ 250,000,000
Share repurchases program, authorized amount (up to)			$ 2,500,000,000.0
Stock repurchase program, remaining authorized repurchase amount	$ 866,000,000
Common stock repurchased (in shares)		3.0