Common Stock (Details) - USD ($) shares in Millions, $ in Millions	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Nov. 30, 2016
Equity, Class of Treasury Stock [Line Items]
Payments for repurchase of common stock	$ 600	$ 625
Stock-based compensation, shares issued during period	4.6	4.5
Common Stock
Equity, Class of Treasury Stock [Line Items]
Common stock repurchased (in shares)	8.0	10.0
Payments for repurchase of common stock	$ 600	$ 625
Share repurchases program, authorized amount (up to)			$ 2,500
Stock repurchase program, remaining authorized repurchase amount	$ 1,800