BORROWED FUNDS - Long Term Debt (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Long-term borrowed funds	$ 14,047	$ 15,925
Parent company
Debt Instrument [Line Items]
Long-term borrowed funds	2,484
Banking Subsidiaries
Debt Instrument [Line Items]
Long-term borrowed funds	$ 11,563
Senior Unsecured Notes \| Parent company \| 2.375% fixed rate senior unsecured debt, due 2021
Debt Instrument [Line Items]
Interest rate	2.375%
Long-term borrowed funds	$ 349	349
Senior Unsecured Notes \| Parent company \| 2.850% fixed-rate senior unsecured notes, due July 2026
Debt Instrument [Line Items]
Interest rate	2.85%
Long-term borrowed funds	$ 496	0
Senior Unsecured Notes \| Banking Subsidiaries \| 2.500% senior unsecured notes, due 2019
Debt Instrument [Line Items]
Interest rate	2.50%
Long-term borrowed funds	$ 0	748
Senior Unsecured Notes \| Banking Subsidiaries \| 2.450% senior unsecured notes, due 2019
Debt Instrument [Line Items]
Interest rate	2.45%
Long-term borrowed funds	$ 0	744
Senior Unsecured Notes \| Banking Subsidiaries \| 2.250% senior unsecured notes, due 2020
Debt Instrument [Line Items]
Interest rate	2.25%
Long-term borrowed funds	$ 700	691
Senior Unsecured Notes \| Banking Subsidiaries \| 2.447% floating-rate senior unsecured notes, due March 2020
Debt Instrument [Line Items]
Interest rate	2.447%
Long-term borrowed funds	$ 300	300
Senior Unsecured Notes \| Banking Subsidiaries \| 2.487% floating-rate senior unsecured notes, due May 2020
Debt Instrument [Line Items]
Interest rate	2.487%
Long-term borrowed funds	$ 250	250
Senior Unsecured Notes \| Banking Subsidiaries \| 2.200% senior unsecured notes, due 2020
Debt Instrument [Line Items]
Interest rate	2.20%
Long-term borrowed funds	$ 500	499
Senior Unsecured Notes \| Banking Subsidiaries \| 2.250% senior unsecured notes, due 2020
Debt Instrument [Line Items]
Interest rate	2.55%
Long-term borrowed funds	$ 750	738
Senior Unsecured Notes \| Banking Subsidiaries \| 2.550% senior unsecured notes, due May 2021
Debt Instrument [Line Items]
Interest rate	2.55%
Long-term borrowed funds	$ 991	964
Senior Unsecured Notes \| Banking Subsidiaries \| 3.250% senior unsecured notes, due February 2022
Debt Instrument [Line Items]
Interest rate	3.25%
Long-term borrowed funds	$ 711	0
Senior Unsecured Notes \| Banking Subsidiaries \| 2.629% floating-rate senior unsecured notes, due February 2022
Debt Instrument [Line Items]
Interest rate	2.629%
Long-term borrowed funds	$ 299	0
Senior Unsecured Notes \| Banking Subsidiaries \| 2.727% floating-rate senior unsecured notes, due May 2022
Debt Instrument [Line Items]
Interest rate	2.727%
Long-term borrowed funds	$ 250	249
Senior Unsecured Notes \| Banking Subsidiaries \| 2.650% senior unsecured notes, due May 2022
Debt Instrument [Line Items]
Interest rate	2.65%
Long-term borrowed funds	$ 501	487
Senior Unsecured Notes \| Banking Subsidiaries \| 3.700% senior unsecured notes, due March 2023
Debt Instrument [Line Items]
Interest rate	3.70%
Long-term borrowed funds	$ 515	502
Senior Unsecured Notes \| Banking Subsidiaries \| 2.911% floating-rate senior unsecured notes, due March 2023
Debt Instrument [Line Items]
Interest rate	2.911%
Long-term borrowed funds	$ 249	249
Senior Unsecured Notes \| Banking Subsidiaries \| 3.750% senior unsecured notes, due February 2026
Debt Instrument [Line Items]
Interest rate	3.75%
Long-term borrowed funds	$ 521	0
Subordinated Debt \| Parent company \| 4.150% fixed rate subordinated debt, due 2022
Debt Instrument [Line Items]
Interest rate	4.15%
Long-term borrowed funds	$ 348	348
Subordinated Debt \| Parent company \| 3.750% fixed rate subordinated debt due 2024
Debt Instrument [Line Items]
Interest rate	3.75%
Long-term borrowed funds	$ 250	250
Subordinated Debt \| Parent company \| 4.023% fixed rate subordinated debt, due 2024
Debt Instrument [Line Items]
Interest rate	4.023%
Long-term borrowed funds	$ 42	42
Subordinated Debt \| Parent company \| 4.350% fixed rate subordinated debt, due 2025
Debt Instrument [Line Items]
Interest rate	4.35%
Long-term borrowed funds	$ 249	249
Subordinated Debt \| Parent company \| 4.300% fixed rate subordinated debt, due 2025
Debt Instrument [Line Items]
Interest rate	4.30%
Long-term borrowed funds	$ 750	749
Federal Home Loan advances \| Banking Subsidiaries
Debt Instrument [Line Items]
Weighted average interest rate	2.006%
Long-term borrowed funds	$ 5,008	7,508
Other \| Banking Subsidiaries
Debt Instrument [Line Items]
Long-term borrowed funds	$ 18	$ 9

Contractual interest rate for funds borrowed, under the debt agreement.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
-Topic 210
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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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