Common Stock (Details) - USD ($) shares in Millions, $ in Millions	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Nov. 30, 2016
Equity, Class of Treasury Stock [Line Items]
Payments for repurchase of common stock	$ 400	$ 410
Stock-based compensation, shares issued during period	3.7	4.1
Common Stock
Equity, Class of Treasury Stock [Line Items]
Common stock repurchased (in shares)	5.4	7.0
Payments for repurchase of common stock	$ 400	$ 425
Share repurchases program, authorized amount (up to)			$ 2,500
Stock repurchase program, remaining authorized repurchase amount	$ 2,000