Derivative Financial Instruments - Notional and Fair Value Amounts of Derivative Financial Instruments (Detail) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Derivative [Line Items]
NOTIONAL VALUE	$ 310,684.3	$ 340,241.0
ASSET	3,151.2	1,902.7
Asset, Total Gross Derivative	3,732.4	2,347.4
Less: Asset, Netting	2,810.7	1,533.8
Derivative Assets	921.7	813.6
LIABILITY	2,548.9	1,566.5
Derivative Liabilities	3,654.1	2,135.2
Less: Liability, Netting	1,865.9	1,283.5
Derivative Liabilities	1,788.2	851.7
Derivatives Designated as Hedging under GAAP
Derivative [Line Items]
NOTIONAL VALUE	8,537.9	12,290.2
ASSET	349.4	252.7
LIABILITY	51.1	33.6
Derivatives Designated as Hedging under GAAP | Fair Value Hedges | Interest Rate Contracts
Derivative [Line Items]
NOTIONAL VALUE	4,622.0	4,430.5
ASSET	58.5	7.6
LIABILITY	32.7	8.7
Derivatives Designated as Hedging under GAAP | Cash Flow Hedges | Foreign Exchange Contracts
Derivative [Line Items]
NOTIONAL VALUE	150.9	3,697.9
ASSET	7.4	61.8
LIABILITY	5.7	12.6
Derivatives Designated as Hedging under GAAP | Net Investment Hedges | Foreign Exchange Contracts
Derivative [Line Items]
NOTIONAL VALUE	3,765.0	4,161.8
ASSET	283.5	183.3
LIABILITY	12.7	12.3
Total Derivatives Not Designated as Hedging under GAAP | Fair Value Hedges
Derivative [Line Items]
NOTIONAL VALUE	302,146.4	327,950.8
ASSET	3,383.0	2,094.7
LIABILITY	3,603.0	2,101.6
Derivatives Not Designated as Hedging under GAAP | Fair Value Hedges
Derivative [Line Items]
NOTIONAL VALUE	773.6	848.4
ASSET	0.4	0.2
LIABILITY	34.9	38.1
Derivatives Not Designated as Hedging under GAAP | Fair Value Hedges | Foreign Exchange Contracts
Derivative [Line Items]
NOTIONAL VALUE	55.9	109.9
ASSET	0.1	0.2
LIABILITY	0.1	0.6
Derivatives Not Designated as Hedging under GAAP | Fair Value Hedges | Other Financial Derivatives
Derivative [Line Items]
NOTIONAL VALUE	717.7	738.5
ASSET	0.3	0.0
LIABILITY	34.8	37.5
Client-Related and Trading Derivatives | Fair Value Hedges
Derivative [Line Items]
NOTIONAL VALUE	301,372.8	327,102.4
ASSET	3,382.6	2,094.5
LIABILITY	3,568.1	2,063.5
Client-Related and Trading Derivatives | Fair Value Hedges | Foreign Exchange Contracts
Derivative [Line Items]
NOTIONAL VALUE	288,994.6	315,532.3
ASSET	3,219.1	1,962.1
LIABILITY	3,169.0	1,973.3
Client-Related and Trading Derivatives | Fair Value Hedges | Interest Rate Contracts
Derivative [Line Items]
NOTIONAL VALUE	12,378.2	11,570.1
ASSET	163.5	132.4
LIABILITY	$ 399.1	$ 90.2