Accumulated Other Comprehensive Income (Loss) (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Jan. 01, 2018
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), net of tax beginning balance			$ (240,400,000)	$ (318,400,000)
Balance, January 1, 2018	$ (252,900,000)	$ (261,600,000)	(252,900,000)	(318,400,000)	$ (316,900,000)
Other comprehensive income (loss), before reclassifications, net of tax			36,000,000.0	7,200,000
Amounts reclassified from accumulated other comprehensive income, net of tax			(48,500,000)	48,100,000
Other comprehensive income (loss), net of tax	(33,500,000)	41,800,000	(12,900,000)	55,000,000.0
Accumulated other comprehensive income (loss), net of tax ending balance	(252,900,000)	(261,600,000)	(252,900,000)	(261,600,000)
Other comprehensive income (loss), net of tax	(33,100,000)	42,300,000	(12,500,000)	55,300,000
Unrealized gains (losses) on securities available for sale
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), net of tax beginning balance			(4,000,000.0)	(1,600,000)
Balance, January 1, 2018	6,200,000	(1,700,000)	(4,000,000.0)	(1,600,000)	(100,000)
Other comprehensive income (loss), before reclassifications, net of tax			11,000,000.0	(7,600,000)
Amounts reclassified from accumulated other comprehensive income, net of tax			(800,000)	6,000,000.0
Other comprehensive income (loss), net of tax			10,200,000	(1,600,000)
Accumulated other comprehensive income (loss), net of tax ending balance	6,200,000	(1,700,000)	6,200,000	(1,700,000)
Unrealized gains (losses) on cash flow hedges
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), net of tax beginning balance			34,700,000	(104,500,000)
Balance, January 1, 2018	13,700,000	(700,000)	34,700,000	(104,500,000)	(104,500,000)
Other comprehensive income (loss), before reclassifications, net of tax			22,300,000	61,700,000
Amounts reclassified from accumulated other comprehensive income, net of tax			(43,300,000)	42,100,000
Other comprehensive income (loss), net of tax			(21,000,000.0)	103,800,000
Accumulated other comprehensive income (loss), net of tax ending balance	13,700,000	(700,000)	13,700,000	(700,000)
Gains (losses) on net investment hedge
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), net of tax beginning balance			3,500,000	0
Balance, January 1, 2018	29,200,000	0	3,500,000	0	0
Other comprehensive income (loss), before reclassifications, net of tax			30,100,000	0
Amounts reclassified from accumulated other comprehensive income, net of tax			(4,400,000)	0
Other comprehensive income (loss), net of tax			25,700,000	0
Accumulated other comprehensive income (loss), net of tax ending balance	29,200,000	0	29,200,000	0
Unfunded status of postretirement benefit plans
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), net of tax beginning balance			(31,300,000)	(36,800,000)
Balance, January 1, 2018	(30,600,000)	(36,400,000)	(31,300,000)	(36,800,000)	(36,800,000)
Other comprehensive income (loss), before reclassifications, net of tax			700,000	400,000
Amounts reclassified from accumulated other comprehensive income, net of tax			0	0
Other comprehensive income (loss), net of tax			700,000	400,000
Accumulated other comprehensive income (loss), net of tax ending balance	(30,600,000)	(36,400,000)	(30,600,000)	(36,400,000)
Currency translation adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), net of tax beginning balance			(243,300,000)	(175,500,000)
Balance, January 1, 2018	(271,400,000)	(222,800,000)	(243,300,000)	(175,500,000)	(175,500,000)
Other comprehensive income (loss), before reclassifications, net of tax			(28,100,000)	(47,300,000)
Amounts reclassified from accumulated other comprehensive income, net of tax			0	0
Other comprehensive income (loss), net of tax			(28,100,000)	(47,300,000)
Accumulated other comprehensive income (loss), net of tax ending balance	$ (271,400,000)	$ (222,800,000)	$ (271,400,000)	$ (222,800,000)
Accounting Standards Update 2016-01
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cumulative effect of new accounting principle in period of adoption					1,500,000
Accounting Standards Update 2016-01 | Unrealized gains (losses) on securities available for sale
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cumulative effect of new accounting principle in period of adoption					1,500,000
Accounting Standards Update 2016-01 | Unrealized gains (losses) on cash flow hedges
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cumulative effect of new accounting principle in period of adoption					0
Accounting Standards Update 2016-01 | Gains (losses) on net investment hedge
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cumulative effect of new accounting principle in period of adoption					0
Accounting Standards Update 2016-01 | Unfunded status of postretirement benefit plans
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cumulative effect of new accounting principle in period of adoption					0
Accounting Standards Update 2016-01 | Currency translation adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cumulative effect of new accounting principle in period of adoption					$ 0