DERIVATIVE INSTRUMENTS AND HEDGING ACTIVITIES - Notional Amounts and Gross Fair Values (Details) - USD ($) $ in Millions	Mar. 31, 2022	Dec. 31, 2021
Derivatives, Fair Value [Line Items]
Notional amount	$ 14,098.0	$ 14,526.0
Derivative asset, not offset against collateral	14.0	3.0
Derivative liability, not offset against collateral	10.0	20.0
Derivative asset, not subject to master netting arrangement	46.0	182.0
Derivative liability, not subject to master netting arrangement	158.0	25.0
Fair value, asset	60.0	185.0
Fair value, liability	168.0	45.0
Interest rate contracts – designated
Derivatives, Fair Value [Line Items]
Derivative asset, not offset against collateral	0.0	1.0
Derivative liability, not offset against collateral	0.0	0.0
Interest rate swaps – not designated
Derivatives, Fair Value [Line Items]
Derivative asset, not offset against collateral	14.0	2.0
Derivative liability, not offset against collateral	10.0	20.0
Derivative asset, not subject to master netting arrangement	37.0	172.0
Derivative liability, not subject to master netting arrangement	145.0	24.0
Interest rate lock commitments – not designated
Derivatives, Fair Value [Line Items]
Derivative asset, not subject to master netting arrangement	0.0	9.0
Derivative liability, not subject to master netting arrangement	13.0	0.0
Forward delivery commitments – not designated
Derivatives, Fair Value [Line Items]
Derivative asset, not subject to master netting arrangement	9.0	1.0
Derivative liability, not subject to master netting arrangement	0.0	1.0
Credit risk contracts – not designated
Derivatives, Fair Value [Line Items]
Notional amount	249.8
Derivative asset, not subject to master netting arrangement	0.0	0.0
Derivative liability, not subject to master netting arrangement	0.0	0.0
Subject to master netting arrangements:
Derivatives, Fair Value [Line Items]
Notional amount	7,449.0	7,627.0
Subject to master netting arrangements: \| Interest rate contracts – designated
Derivatives, Fair Value [Line Items]
Notional amount	1,980.0	2,080.0
Subject to master netting arrangements: \| Interest rate swaps – not designated
Derivatives, Fair Value [Line Items]
Notional amount	5,469.0	5,547.0
Not subject to master netting arrangements:
Derivatives, Fair Value [Line Items]
Notional amount	6,649.0	6,899.0
Not subject to master netting arrangements: \| Interest rate swaps – not designated
Derivatives, Fair Value [Line Items]
Notional amount	5,469.0	5,547.0
Not subject to master netting arrangements: \| Interest rate lock commitments – not designated
Derivatives, Fair Value [Line Items]
Notional amount	381.0	482.0
Not subject to master netting arrangements: \| Forward delivery commitments – not designated
Derivatives, Fair Value [Line Items]
Notional amount	435.0	502.0
Not subject to master netting arrangements: \| Credit risk contracts – not designated
Derivatives, Fair Value [Line Items]
Notional amount	$ 364.0	$ 368.0

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Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset.

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