Derivative Financial Instruments - Location and Amount of Fair Value Hedge Derivative Gains and Losses Recorded in Income (Detail) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Derivative Instruments, Gain (Loss) [Line Items]
Interest Income	$ 1,643.5	$ 2,877.7	$ 1,406.5	$ 1,643.5
Interest Expense	200.3	990.5	23.8	200.3
Other Operating Income	194.0	191.3	243.9	$ 194.0
INTEREST INCOME
Derivative Instruments, Gain (Loss) [Line Items]
Total gains (losses) recognized on fair value hedges	(13.2)	(4.4)	(16.2)
Total gain/(loss) recognized on cash flow hedges	27.9	0.6	10.5
INTEREST EXPENSE
Derivative Instruments, Gain (Loss) [Line Items]
Total gains (losses) recognized on fair value hedges	29.9	24.1	57.1
Total gain/(loss) recognized on cash flow hedges	0.0	0.0	0.0
OTHER OPERATING INCOME
Derivative Instruments, Gain (Loss) [Line Items]
Total gains (losses) recognized on fair value hedges	0.0	0.0	0.0
Total gain/(loss) recognized on cash flow hedges	0.2	(4.3)	(6.0)
Interest Rate Contracts | INTEREST INCOME
Derivative Instruments, Gain (Loss) [Line Items]
Interest Rate Contracts, Recognized on Derivatives	(66.3)	82.8	39.1
Interest Rate Contracts, Recognized on Hedged Items	66.3	(82.8)	(39.1)
Interest Rate Contracts, Amounts Related to Interest Settlements on Derivatives	(13.2)	(4.4)	(16.2)
Total gain/(loss) recognized on cash flow hedges	0.5	0.0	0.0
Interest Rate Contracts | INTEREST EXPENSE
Derivative Instruments, Gain (Loss) [Line Items]
Interest Rate Contracts, Recognized on Derivatives	100.2	(373.4)	(161.6)
Interest Rate Contracts, Recognized on Hedged Items	(100.2)	373.4	161.6
Interest Rate Contracts, Amounts Related to Interest Settlements on Derivatives	29.9	24.1	57.1
Total gain/(loss) recognized on cash flow hedges	0.0	0.0	0.0
Interest Rate Contracts | OTHER OPERATING INCOME
Derivative Instruments, Gain (Loss) [Line Items]
Interest Rate Contracts, Recognized on Derivatives	0.0	0.0	0.0
Interest Rate Contracts, Recognized on Hedged Items	0.0	0.0	0.0
Interest Rate Contracts, Amounts Related to Interest Settlements on Derivatives	0.0	0.0	0.0
Total gain/(loss) recognized on cash flow hedges	0.0	0.0	0.0
Foreign Exchange Contracts | INTEREST INCOME
Derivative Instruments, Gain (Loss) [Line Items]
Total gain/(loss) recognized on cash flow hedges	27.4	0.6	10.5
Foreign Exchange Contracts | INTEREST EXPENSE
Derivative Instruments, Gain (Loss) [Line Items]
Total gain/(loss) recognized on cash flow hedges	0.0	0.0	0.0
Foreign Exchange Contracts | OTHER OPERATING INCOME
Derivative Instruments, Gain (Loss) [Line Items]
Total gain/(loss) recognized on cash flow hedges	$ 0.2	$ (4.3)	$ (6.0)