Stock Repurchases (Details) - USD ($) shares in Millions		3 Months Ended
	Feb. 08, 2018	Mar. 31, 2018	Mar. 31, 2017	Mar. 16, 2018
Stockholders' Equity Note [Abstract]
Stock repurchase program, authorized amount		$ 2,500,000,000.0		$ 500,000,000
Stock repurchase program, remaining authorized amount		$ 746,000,000
Accelerated share repurchases, initial price to be paid	$ 150,000,000
Accelerated share repurchases, percentage of shares to be repurchased	85.00%
Accelerated share repurchases, number of shares	0.7
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		$ 18,100,000	$ 13,300,000