Treasury Stock (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Equity, Class of Treasury Stock [Line Items]
Stock repurchase program, authorized amount	$ 6,800,000,000		$ 6,800,000,000
Available to repurchase common stock	404,000,000		404,000,000
Amount expended on share repurchases in open market transactions	$ 0	$ 0	$ 500,000,000	$ 28,700,000
Number of shares repurchased			6,399,499	426,300
Average per share price on share repurchases in open market transactions (in dollars per share)			$ 78.13	$ 67.30
Number of shares withheld to satisfy minimum tax withholding obligations	43,446	134,771	734,600	563,609
Payment for tax withholding related to vested stock units	$ 3,600,000	$ 11,000,000	$ 60,500,000	$ 43,900,000
Amount Authorized in January 2017 [Member]
Equity, Class of Treasury Stock [Line Items]
Stock repurchase program, authorized amount	$ 500,000,000		$ 500,000,000