Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), net of tax beginning balance			$ (135.2)	$ (240.4)
Balance, January 1, 2018	$ (225.5)	$ (92.3)	(225.5)	(92.3)
Other comprehensive income (loss), before reclassifications, net of tax			(54.4)	233.7
Amounts reclassified from accumulated other comprehensive income, net of tax			(35.9)	(85.6)
Other comprehensive income (loss), net of tax	(45.4)	160.6	(89.4)	147.7
Accumulated other comprehensive income (loss), net of tax ending balance	(225.5)	(92.3)	(225.5)	(92.3)
Other comprehensive income (loss), net of tax	(44.5)	160.6	(90.3)	148.1
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			4.2	(4.0)
Balance, January 1, 2018	5.2	6.3	5.2	6.3
Other comprehensive income (loss), before reclassifications, net of tax			(8.8)	11.6
Amounts reclassified from accumulated other comprehensive income, net of tax			9.8	(1.3)
Other comprehensive income (loss), net of tax			1.0	10.3
Accumulated other comprehensive income (loss), net of tax ending balance	5.2	6.3	5.2	6.3
Unrealized gains (losses) on cash flow hedges
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), net of tax beginning balance			7.8	34.7
Balance, January 1, 2018	(93.3)	72.8	(93.3)	72.8
Other comprehensive income (loss), before reclassifications, net of tax			(58.0)	115.8
Amounts reclassified from accumulated other comprehensive income, net of tax			(43.1)	(77.7)
Other comprehensive income (loss), net of tax			(101.1)	38.1
Accumulated other comprehensive income (loss), net of tax ending balance	(93.3)	72.8	(93.3)	72.8
Gains (losses) on net investment hedge
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), net of tax beginning balance			25.1	3.5
Balance, January 1, 2018	30.6	50.4	30.6	50.4
Other comprehensive income (loss), before reclassifications, net of tax			8.1	53.5
Amounts reclassified from accumulated other comprehensive income, net of tax			(2.6)	(6.6)
Other comprehensive income (loss), net of tax			5.5	46.9
Accumulated other comprehensive income (loss), net of tax ending balance	30.6	50.4	30.6	50.4
Unfunded status of postretirement benefit plans
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), net of tax beginning balance			(32.8)	(31.3)
Balance, January 1, 2018	(32.4)	(29.8)	(32.4)	(29.8)
Other comprehensive income (loss), before reclassifications, net of tax			0.4	1.5
Amounts reclassified from accumulated other comprehensive income, net of tax			0.0	0.0
Other comprehensive income (loss), net of tax			0.4	1.5
Accumulated other comprehensive income (loss), net of tax ending balance	(32.4)	(29.8)	(32.4)	(29.8)
Currency translation adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), net of tax beginning balance			(139.5)	(243.3)
Balance, January 1, 2018	(135.6)	(192.0)	(135.6)	(192.0)
Other comprehensive income (loss), before reclassifications, net of tax			3.9	51.3
Amounts reclassified from accumulated other comprehensive income, net of tax			0.0	0.0
Other comprehensive income (loss), net of tax			3.9	51.3
Accumulated other comprehensive income (loss), net of tax ending balance	$ (135.6)	$ (192.0)	$ (135.6)	$ (192.0)