Fair Value Measurements and Risk - Gain (Loss) on Derivative Instruments (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Gains and losses on derivative instruments
Interest and Debt Expense	$ (18,600,000)	$ (20,400,000)	$ (58,200,000)	$ (59,600,000)
Nonoperating Income (Expense)	1,100,000	2,300,000	3,200,000	(300,000)
Cash Flow Hedging
Gains and losses on derivative instruments
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), before Reclassification and Tax	28,100,000	(600,000)	26,900,000	29,000,000.0
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	29,100,000	(3,300,000)	39,300,000	32,500,000
Cash Flow Hedging | Interest rate derivatives
Gains and losses on derivative instruments
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), before Reclassification and Tax	(500,000)	800,000	(3,400,000)	2,800,000
Cash Flow Hedging | Interest rate derivatives | Interest expense
Gains and losses on derivative instruments
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	(200,000)	100,000	(200,000)	0
Cash Flow Hedging | 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
Cash Flow Hedging | Currency contracts
Gains and losses on derivative instruments
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), before Reclassification and Tax	3,800,000	(600,000)	4,600,000	2,500,000
Gain (Loss) from Components Excluded from Assessment of Cash Flow Hedge Effectiveness, Net	700,000	700,000	2,100,000	1,100,000
Cash Flow Hedging | 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
Derivative Instruments, Gain (Loss) Recognized in Income, Ineffective Portion and Amount Excluded from Effectiveness Testing, Net	0	0	0	0
Cash Flow Hedging | Currency contracts | Other expense
Gains and losses on derivative instruments
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	3,800,000	(600,000)	3,800,000	2,900,000
Derivative Instruments, Gain (Loss) Recognized in Income, Ineffective Portion and Amount Excluded from Effectiveness Testing, Net	700,000	600,000	2,100,000	2,300,000
Cash Flow Hedging | 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	2,500,000	3,300,000	400,000	6,400,000
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	3,200,000	3,300,000	10,400,000	6,400,000
Cash Flow Hedging | 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	22,300,000	(4,100,000)	25,300,000	17,300,000
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	22,300,000	(6,100,000)	25,300,000	23,200,000
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	(1,200,000)	(200,000)	(1,100,000)	(2,900,000)
Net Investment Hedging [Member]
Gains and losses on derivative instruments
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	0	0	0	0
Net Investment Hedging [Member] | Currency Swap [Member]
Gains and losses on derivative instruments
Derivative Instruments, Gain (Loss) Recognized in Income, Ineffective Portion and Amount Excluded from Effectiveness Testing, Net	$ 900,000	$ 700,000	$ 2,500,000	$ 1,500,000