Accumulated Other Comprehensive Income (Loss) - Summary of Changes in Accumulated Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, beginning of period	$ 11,688.3	$ 11,091.0	$ 10,508.3
Net Change	(463.6)	622.7	259.0
Balance, end of period	12,016.8	11,688.3	11,091.0
TOTAL
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, beginning of period	428.0	(194.7)	(453.7)
Balance, end of period	(35.6)	428.0	(194.7)
NET UNREALIZED GAINS (LOSSES) ON AVAILABLE FOR SALE DEBT SECURITIES
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, beginning of period	641.8	114.0	(114.9)
Net Change	(534.7)	527.8	228.9
Balance, end of period	107.1	641.8	114.0
NET UNREALIZED (LOSSES) GAINS ON CASH FLOW HEDGES
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, beginning of period	(3.2)	(3.7)	4.0
Net Change	0.8	0.5	(7.7)
Balance, end of period	(2.4)	(3.2)	(3.7)
NET FOREIGN CURRENCY ADJUSTMENT
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, beginning of period	144.7	117.8	67.9
Net Change	10.5	26.9	49.9
Balance, end of period	155.2	144.7	117.8
NET PENSION AND OTHER POSTRETIREMENT BENEFIT ADJUSTMENTS
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, beginning of period	(355.3)	(422.8)	(410.7)
Net Change	59.8	67.5	(12.1)
Balance, end of period	$ (295.5)	$ (355.3)	$ (422.8)