LOANS AND ALLOWANCE FOR CREDIT LOSSES (Age Analysis of Past Due Loans) (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Financing Receivable, Past Due [Line Items]
Total Past Due	$ 3,519,814	$ 5,720,325
Current	90,404,870	88,405,338
Total	93,924,684	94,125,663
Recorded Investment Greater than 90 Days and Accruing	45,117	93,102
LHFS	240,200	289,000
30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	2,920,822	4,841,015
90 Days or Greater
Financing Receivable, Past Due [Line Items]
Total Past Due	598,992	879,310
Commercial
Financing Receivable, Past Due [Line Items]
Total	39,795,462	41,151,009
LHFS	144,100	116,300
Commercial | CRE
Financing Receivable, Past Due [Line Items]
Total Past Due	94,864	116,762
Current	7,372,034	8,351,261
Total	7,466,898	8,468,023
Recorded Investment Greater than 90 Days and Accruing	0	0
Commercial | CRE | 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	27,468	51,472
Commercial | CRE | 90 Days or Greater
Financing Receivable, Past Due [Line Items]
Total Past Due	67,396	65,290
Commercial | C&I
Financing Receivable, Past Due [Line Items]
Total Past Due	117,886	140,597
Current	16,315,919	16,510,391
Total	16,433,805	16,650,988
Recorded Investment Greater than 90 Days and Accruing	0	0
LHFS	144,100
Commercial | C&I | 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	54,832	55,957
Commercial | C&I | 90 Days or Greater
Financing Receivable, Past Due [Line Items]
Total Past Due	63,054	84,640
Commercial | Multifamily
Financing Receivable, Past Due [Line Items]
Total Past Due	47,542	14,160
Current	8,629,941	8,627,044
Total	8,677,483	8,641,204
Recorded Investment Greater than 90 Days and Accruing	0	0
Commercial | Multifamily | 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	37,822	10,456
Commercial | Multifamily | 90 Days or Greater
Financing Receivable, Past Due [Line Items]
Total Past Due	9,720	3,704
Commercial | Other commercial
Financing Receivable, Past Due [Line Items]
Total Past Due	148,802	68,325
Current	7,068,474	7,322,469
Total	7,217,276	7,390,794
Recorded Investment Greater than 90 Days and Accruing	47	0
Commercial | Other commercial | 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	142,627	61,973
Commercial | Other commercial | 90 Days or Greater
Financing Receivable, Past Due [Line Items]
Total Past Due	6,175	6,352
Consumer | Residential mortgages
Financing Receivable, Past Due [Line Items]
Total Past Due	190,428	283,556
Current	7,182,040	8,848,971
Total	7,372,468	9,132,527
Recorded Investment Greater than 90 Days and Accruing	0	0
LHFS	240,200	296,800
Consumer | Residential mortgages | 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	78,452	154,978
Consumer | Residential mortgages | 90 Days or Greater
Financing Receivable, Past Due [Line Items]
Total Past Due	111,976	128,578
Consumer | Home equity loans and lines of credit
Financing Receivable, Past Due [Line Items]
Total Past Due	104,127	121,389
Current	4,184,399	4,648,955
Total	4,288,526	4,770,344
Recorded Investment Greater than 90 Days and Accruing	0	0
Consumer | Home equity loans and lines of credit | 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	37,688	45,417
Consumer | Home equity loans and lines of credit | 90 Days or Greater
Financing Receivable, Past Due [Line Items]
Total Past Due	66,439	75,972
Consumer | RICs and auto loans
Financing Receivable, Past Due [Line Items]
Total Past Due	2,699,293	4,768,833
Current	37,916,538	31,687,914
Total	40,615,831	36,456,747
Recorded Investment Greater than 90 Days and Accruing	0	0
Consumer | RICs and auto loans | 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	2,481,517	4,364,110
Consumer | RICs and auto loans | 90 Days or Greater
Financing Receivable, Past Due [Line Items]
Total Past Due	217,776	404,723
Consumer | Personal unsecured loans
Financing Receivable, Past Due [Line Items]
Total Past Due	100,744	187,849
Current	1,508,408	2,110,803
Total	1,609,152	2,298,652
Recorded Investment Greater than 90 Days and Accruing	45,070	93,102
LHFS	763,300	1,000,000
Consumer | Personal unsecured loans | 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	51,253	85,277
Consumer | Personal unsecured loans | 90 Days or Greater
Financing Receivable, Past Due [Line Items]
Total Past Due	49,491	102,572
Consumer | Other consumer
Financing Receivable, Past Due [Line Items]
Total Past Due	16,128	18,854
Current	227,117	297,530
Total	243,245	316,384
Recorded Investment Greater than 90 Days and Accruing	0	0
Consumer | Other consumer | 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	9,163	11,375
Consumer | Other consumer | 90 Days or Greater
Financing Receivable, Past Due [Line Items]
Total Past Due	$ 6,965	$ 7,479