Stock Repurchases (Details) - USD ($) shares in Millions			6 Months Ended
	Apr. 28, 2017	Feb. 09, 2017	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Stockholders' Equity Note [Abstract]
Stock repurchase program, authorized amount			$ 2,000,000,000		$ 550,000,000
Stock repurchase program, remaining authorized amount			$ 471,000,000
Accelerated share repurchases, initial price to be paid	$ 100,000,000	$ 75,000,000
Accelerated share repurchases, percentage of shares to be repurchased	85.00%	85.00%
Accelerated share repurchases, number of shares	0.5	0.5
Shares repurchased from employees who surrendered shares to satisfy minimum tax withholding obligations			0.1
Shares repurchased from employees who surrendered shares to satisfy minimum tax withholding obligations, value			$ 14,100,000	$ 21,400,000