Accumulated Other Comprehensive Income (Loss) (Summary of Changes in Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended						9 Months Ended
	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2022	Sep. 30, 2021
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	$ 11,069.7	$ 11,409.8	$ 12,016.8	$ 11,823.0	$ 11,457.9	$ 11,688.3	$ 12,016.8	$ 11,688.3
Net Change	(274.4)	(603.6)	(871.4)	(80.7)	128.8	(362.1)	(1,749.4)	(314.0)
Ending balance	11,030.4	11,069.7	11,409.8	11,898.8	11,823.0	11,457.9	11,030.4	11,898.8
TOTAL
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	(1,510.6)	(907.0)	(35.6)	194.7	65.9	428.0	(35.6)	428.0
Net Change	(274.4)	(603.6)	(871.4)	(80.7)	128.8	(362.1)
Ending balance	(1,785.0)	(1,510.6)	(907.0)	114.0	194.7	65.9	(1,785.0)	114.0
NET UNREALIZED GAINS (LOSSES) ON AVAILABLE FOR SALE DEBT SECURITIES
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	(1,294.7)		107.1	373.0		641.8	107.1	641.8
Net Change	(272.2)			(89.6)			(1,674.0)	(358.4)
Ending balance	(1,566.9)	(1,294.7)		283.4	373.0		(1,566.9)	283.4
NET UNREALIZED (LOSSES) GAINS ON CASH FLOW HEDGES
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	0.6		(2.4)	(5.4)		(3.2)	(2.4)	(3.2)
Net Change	2.1			4.6			5.1	2.4
Ending balance	2.7	0.6		(0.8)	(5.4)		2.7	(0.8)
NET FOREIGN CURRENCY ADJUSTMENT
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	137.6		155.2	151.8		144.7	155.2	144.7
Net Change	20.2			3.8			2.6	10.9
Ending balance	157.8	137.6		155.6	151.8		157.8	155.6
NET PENSION AND OTHER POSTRETIREMENT BENEFIT ADJUSTMENTS
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	(354.1)		$ (295.5)	(324.7)		$ (355.3)	(295.5)	(355.3)
Net Change	(24.5)			0.5			(83.1)	31.1
Ending balance	$ (378.6)	$ (354.1)		$ (324.2)	$ (324.7)		$ (378.6)	$ (324.2)