Stockholders' Deficit (Narrative) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	1 Months Ended	3 Months Ended
	Feb. 11, 2016	Mar. 31, 2017
Treasury Stock Repurchase Programs [Line Items]
Additional share repurchase amount authorized	$ 640.9
Remaining common stock available for repurchase	$ 359.1	$ 920.1
Common stock, held in treasury		223.1
Common stock repurchased		$ 8,300.0
Share Buyback Program [Member]
Treasury Stock Repurchase Programs [Line Items]
Common stock authorized to repurchase		$ 1,000.0
Common stock repurchase, share		1.8
Average stock price		$ 82.25
Aggregate cost of share		$ 150.0
Restricted Stock Units [Member]
Treasury Stock Repurchase Programs [Line Items]
Common stock repurchase, share		0.3
Average stock price		$ 82.63
Aggregate cost of share		$ 23.0