Equity, Stock Repurchase Program (Details) - USD ($) shares in Millions, $ in Millions		1 Months Ended			12 Months Ended
	Jan. 24, 2017	Feb. 10, 2017	Jan. 31, 2015	Jan. 31, 2013	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
2013 Stock Repurchase Program
Stock-Based Compensation
Number of shares authorized to be repurchased under the current open-market stock repurchase program				20.0
Repurchase of stock program, period				2 years
Number of shares repurchased and retired							11.4
Payments for shares repurchased and retired (in dollars)							$ 539.4
2015 Stock Repurchase Program
Stock-Based Compensation
Number of shares authorized to be repurchased under the current open-market stock repurchase program			10.0
Repurchase of stock program, period			2 years
Number of shares repurchased and retired					5.5	4.5
Payments for shares repurchased and retired (in dollars)					$ 325.8	$ 248.9
2017 Stock Repurchase Program
Stock-Based Compensation
Repurchase of stock program, period	2 years
Number of shares repurchased		3.2
Payments for shares repurchased (in dollars)		$ 213.9
Value of shares authorized to be repurchased	$ 1,000.0