Shareholders' Equity, Stock Repurchase (Details) - 2017 Stock Repurchase Program - USD ($) $ in Millions		1 Months Ended	9 Months Ended
	Jan. 24, 2017	Oct. 31, 2017	Sep. 30, 2017
Shareholders' Equity
Value of shares authorized to be repurchased	$ 1,000.0
Repurchase of stock program, period	2 years
Number of shares repurchased and retired			7,700,000
Payments for shares repurchased and retired (in dollars)			$ 555.6
Value of shares remaining that may be repurchased under the stock repurchase program		$ 444.4
Number of shares repurchased		0