Treasury Stock (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 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	329,000,000		329,000,000
Amount expended on share repurchases in open market transactions	$ 75,000,000	$ 0	$ 575,000,000	$ 28,700,000
Number of shares repurchased	984,869		7,384,368	426,300
Average per share price on share repurchases in open market transactions (in dollars per share)	$ 76.11		$ 77.86	$ 67.30
Number of shares withheld to satisfy minimum tax withholding obligations	135,003	134,782	870,656	698,391
Payment for tax withholding related to vested stock units	$ 10,600,000	$ 12,000,000	$ 71,200,000	$ 55,000,000
Amount Authorized in January 2017 [Member]
Equity, Class of Treasury Stock [Line Items]
Stock repurchase program, authorized amount	$ 500,000,000		$ 500,000,000