Stockholders' Deficit (Narrative) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2018	Feb. 08, 2018
Treasury Stock Repurchase Programs [Line Items]
Additional share repurchase amount authorized		$ 585.8
Remaining common stock available for repurchase	$ 638.3	$ 638.3	$ 414.2
Common stock, held in treasury	231.1	231.1
Common stock repurchased	$ 9,200.0	$ 9,200.0
Share Buyback Program [Member]
Treasury Stock Repurchase Programs [Line Items]
Common stock authorized to repurchase			$ 1,000.0
Common stock repurchase, share	1.1	3.2
Average stock price	$ 152.21	$ 133.30
Aggregate cost of share	$ 175.0	$ 424.9
Restricted Stock Units [Member]
Treasury Stock Repurchase Programs [Line Items]
Common stock repurchase, share		0.3
Average stock price		$ 121.40
Aggregate cost of share		$ 34.9

Amount of stock repurchase plan authorized.

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Amount remaining of a stock repurchase plan authorized.

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Total cost of shares repurchased divided by the total number of shares repurchased.

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Number of common and preferred shares that were previously issued and that were repurchased by the issuing entity and held in treasury on the financial statement date. This stock has no voting rights and receives no dividends.

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Number of shares that have been repurchased during the period and are being held in treasury.

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The amount allocated to treasury stock. Treasury stock is common and preferred shares of an entity that were issued, repurchased by the entity, and are held in its treasury.

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Equity impact of the cost of common and preferred stock that were repurchased during the period. Recorded using the cost method.

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