Accumulated Other Comprehensive Income (Loss) (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 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	$ (92,300,000)	$ (248,300,000)	(92,300,000)	(318,400,000)	$ (316,900,000)
Other comprehensive income (loss), before reclassifications, net of tax			233,700,000	11,800,000
Amounts reclassified from accumulated other comprehensive income, net of tax			(85,600,000)	56,800,000
Other comprehensive income (loss), net of tax	160,600,000	13,300,000	147,700,000	68,300,000
Accumulated other comprehensive income (loss), net of tax ending balance	(92,300,000)	(248,300,000)	(92,300,000)	(248,300,000)
Other comprehensive income (loss), net of tax	160,600,000	13,300,000	148,100,000	68,600,000
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	6,300,000	(1,900,000)	(4,000,000.0)	(1,600,000)	(100,000)
Other comprehensive income (loss), before reclassifications, net of tax			11,600,000	(7,900,000)
Amounts reclassified from accumulated other comprehensive income, net of tax			(1,300,000)	6,100,000
Other comprehensive income (loss), net of tax			10,300,000	(1,800,000)
Accumulated other comprehensive income (loss), net of tax ending balance	6,300,000	(1,900,000)	6,300,000	(1,900,000)
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	72,800,000	4,500,000	34,700,000	(104,500,000)	(104,500,000)
Other comprehensive income (loss), before reclassifications, net of tax			115,800,000	58,300,000
Amounts reclassified from accumulated other comprehensive income, net of tax			(77,700,000)	50,700,000
Other comprehensive income (loss), net of tax			38,100,000	109,000,000.0
Accumulated other comprehensive income (loss), net of tax ending balance	72,800,000	4,500,000	72,800,000	4,500,000
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	50,400,000	0	3,500,000	0	0
Other comprehensive income (loss), before reclassifications, net of tax			53,500,000	0
Amounts reclassified from accumulated other comprehensive income, net of tax			(6,600,000)	0
Other comprehensive income (loss), net of tax			46,900,000	0
Accumulated other comprehensive income (loss), net of tax ending balance	50,400,000	0	50,400,000	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	(29,800,000)	(36,600,000)	(31,300,000)	(36,800,000)	(36,800,000)
Other comprehensive income (loss), before reclassifications, net of tax			1,500,000	200,000
Amounts reclassified from accumulated other comprehensive income, net of tax			0	0
Other comprehensive income (loss), net of tax			1,500,000	200,000
Accumulated other comprehensive income (loss), net of tax ending balance	(29,800,000)	(36,600,000)	(29,800,000)	(36,600,000)
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	(192,000,000.0)	(214,300,000)	(243,300,000)	(175,500,000)	(175,500,000)
Other comprehensive income (loss), before reclassifications, net of tax			51,300,000	(38,800,000)
Amounts reclassified from accumulated other comprehensive income, net of tax			0	0
Other comprehensive income (loss), net of tax			51,300,000	(38,800,000)
Accumulated other comprehensive income (loss), net of tax ending balance	$ (192,000,000.0)	$ (214,300,000)	$ (192,000,000.0)	$ (214,300,000)
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