Summary of Significant Accounting Policies New Accounting Standards (Details) - USD ($) $ in Millions	Dec. 31, 2020	Jan. 01, 2020	Dec. 31, 2019		Jan. 01, 2019	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Right-of-use assets, net	$ 322.0		$ 270.3
Lease liabilities	344.4
Cumulative effect of change in accounting principle	202.5		207.6			$ 166.6		$ 338.2
Cumulative Effect, Period of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of change in accounting principle			(1.7)	[1]				2.2
Retained Earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of change in accounting principle	$ 407.5		457.4			$ 429.1		564.9
Retained Earnings | Cumulative Effect, Period of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of change in accounting principle			$ (1.7)	[1]				$ 3.3
Accounting Standards Update 2014-09 | Retained Earnings | Cumulative Effect, Period of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of change in accounting principle							$ 1.5
Accounting Standards Update 2016-01 | Retained Earnings | Cumulative Effect, Period of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of change in accounting principle							1.1
Accounting Standards Update 2016-16 | Retained Earnings | Cumulative Effect, Period of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of change in accounting principle							$ 0.7
Accounting Standards Update 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Right-of-use assets, net					$ 310.1
Lease liabilities					320.3
Accounting Standards Update 2016-13 | Retained Earnings | Cumulative Effect, Period of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of change in accounting principle		$ 1.7
Accounting Standards Update 2018-02 | Retained Earnings | Cumulative Effect, Period of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of change in accounting principle					$ 28.8

[1] Effective January 1, 2019, we adopted the provisions of ASU 2018-02, Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income. We recognized a cumulative effect adjustment to January 1, 2019 retained earnings as a result of adopting this standard. See Note 1 for further details.(c)Effective January 1, 2020, we adopted the provisions of ASU 2016-13, Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments. We recognized a cumulative effect adjustment to January 1, 2020 retained earnings as a result of adopting this standard. See Note 1 for further details.