Fair Value Measurements and Risk - Gain (Loss) on Derivative Instruments (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Cash Flow Hedging [Member]
Gains and losses on derivative instruments
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), before Reclassification and Tax	$ (20.9)	$ 28.1	$ (18.6)	$ 26.9
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	(22.7)	29.1	(18.4)	39.3
Cash Flow Hedging [Member] | Interest rate derivatives
Gains and losses on derivative instruments
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), before Reclassification and Tax	(0.3)	(0.5)	(3.8)	(3.4)
Cash Flow Hedging [Member] | Interest rate derivatives | Interest expense
Gains and losses on derivative instruments
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	(0.6)	(0.2)	(1.2)	(0.2)
Cash Flow Hedging [Member] | Interest rate derivatives | Other expense
Gains and losses on derivative instruments
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	0.0	0.0	0.0	0.0
Cash Flow Hedging [Member] | Currency contracts
Gains and losses on derivative instruments
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), before Reclassification and Tax		3.8	2.7	4.6
Cash Flow Hedging [Member] | Currency contracts | Interest expense
Gains and losses on derivative instruments
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	0.0	0.0	0.0	0.0
Cash Flow Hedging [Member] | Currency contracts | Other expense
Gains and losses on derivative instruments
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	0.0	3.8	3.2	3.8
Cash Flow Hedging [Member] | Variable-to-fixed cross-currency swaps | Interest expense
Gains and losses on derivative instruments
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), before Reclassification and Tax	1.4	2.5	7.1	0.4
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	(0.1)	3.2	4.2	10.4
Cash Flow Hedging [Member] | Variable-to-fixed cross-currency swaps | Other expense
Gains and losses on derivative instruments
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), before Reclassification and Tax	(22.0)	22.3	(24.6)	25.3
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	(22.0)	22.3	(24.6)	25.3
Derivatives not designated as hedging instruments under ASC 815: | Currency contracts | Other expense
Gains and losses on derivative instruments
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	$ (1.4)	(1.2)	(2.2)	(1.1)
AOCI, Derivative Qualifying as Hedge, Excluded Component, Parent [Member] | Cash Flow Hedging [Member] | Currency contracts
Gains and losses on derivative instruments
Other Comprehensive Income (Loss), Derivative, Excluded Component, Increase (Decrease), before Adjustments and Tax		$ 0.7	$ (0.6)	$ 2.1