Derivative Financial Instruments - Location and Amount of Fair Value Hedge Derivative Gains and Losses Recorded in Income (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Derivative Instruments, Gain (Loss) [Line Items]
Interest Income	$ 8,624.6	$ 9,762.3	$ 7,325.0
Interest Expense	6,213.6	7,585.2	5,343.0
Other Operating Income	207.7	1,157.4	228.7
INTEREST INCOME
Derivative Instruments, Gain (Loss) [Line Items]
Total gains (losses) recognized on fair value hedges	30.9	96.6	47.1
Total gain/(loss) recognized on cash flow hedges	20.5	13.4	34.9
INTEREST EXPENSE
Derivative Instruments, Gain (Loss) [Line Items]
Total gains (losses) recognized on fair value hedges	(58.6)	(76.9)	(86.5)
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	0.0	0.0	1.9
Interest Rate Contracts | INTEREST INCOME
Derivative Instruments, Gain (Loss) [Line Items]
Interest Rate Contracts, Recognized on Derivatives	(139.7)	126.6	(132.6)
Interest Rate Contracts, Recognized on Hedged Items	139.7	(126.6)	132.6
Interest Rate Contracts, Amounts Related to Interest Settlements on Derivatives	30.9	96.6	47.1
Interest Rate Contracts | INTEREST EXPENSE
Derivative Instruments, Gain (Loss) [Line Items]
Interest Rate Contracts, Recognized on Derivatives	72.8	(5.1)	74.9
Interest Rate Contracts, Recognized on Hedged Items	(72.8)	5.1	(74.9)
Interest Rate Contracts, Amounts Related to Interest Settlements on Derivatives	(58.6)	(76.9)	(86.5)
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
Foreign Exchange Contracts | INTEREST INCOME
Derivative Instruments, Gain (Loss) [Line Items]
Total gain/(loss) recognized on cash flow hedges	20.5	13.4	34.9
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	$ 0.0	$ 0.0	$ 1.9