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Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Equity Based Compensation (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options, Exercises in Period, Total Intrinsic Value	$ 42.1	$ 41.4	$ 26.2
Performance Contingent Unit Share Payout	0.75	0.400
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized, Period for Recognition	1 year 6 months
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized	$ 26.3
Performance Contingent Units Measurement Period	3 years
Allocated Share-based Compensation Expense	$ 22.3	$ 33.1	$ 16.0
Options, Grants in Period, Weighted Average Exercise Price	$ 129.72	$ 93.53	$ 91.65
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Expirations in Period	430,429,000
Expiration Period	10 years
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Net of Forfeitures	171,388,000
Options, Grants in Period, Weighted Average Exercise Price	$ 129.72
Flexible Stock Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number Of Shares Available For Grant	14,960,077
Flexible Stock Plan For Directors [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number Of Shares Available For Grant	412,500
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Expirations in Period	137,083	94,436
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Net of Forfeitures	115,176
Options, Grants in Period, Weighted Average Exercise Price	$ 129.72
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Expirations in Period	38,843
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Net of Forfeitures	22,971
Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting Period	1 year
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting Period	5 years