LOANS AND LEASES - Origination Year (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2023	Dec. 31, 2022
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year		$ 1,227.0	$ 7,061.0
Fiscal year before current fiscal year		6,938.0	6,630.0
Two years before current fiscal year		6,574.0	4,128.0
Three years before current fiscal year		4,036.0	2,669.0
Four years before current fiscal year		2,573.0	1,571.0
Prior		6,020.0	4,816.0
Revolving Loans Amortized Cost Basis		3,305.0	3,380.0
Total Loans and Leases	[1]	30,673.0	30,255.0
Current fiscal year, writeoff		0.0
Fiscal year before current fiscal year, writeoff		1.2
Two years before current fiscal year, writeoff		1.5
Three years before current fiscal year, writeoff		0.5
Four years before current fiscal year, writeoff		0.6
Prior, writeoff		12.9
Revolving Loans Amortized Cost Basis, writeoff		0.0
Total Loans and Leases, writeoff		16.7
Current
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases		30,490.0	30,039.0
Past due
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases		183.0	216.0
Total commercial loans and leases
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year		766.0	3,915.0
Fiscal year before current fiscal year		3,777.0	3,766.0
Two years before current fiscal year		3,774.0	2,629.0
Three years before current fiscal year		2,590.0	2,033.0
Four years before current fiscal year		1,965.0	1,261.0
Prior		4,384.0	3,397.0
Revolving Loans Amortized Cost Basis		2,256.0	2,289.0
Total Loans and Leases		19,512.0	19,290.0
Total commercial loans and leases | Current
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases		19,409.0	19,179.0
Total commercial loans and leases | Past due
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases		103.0	111.0
Total commercial loans and leases | Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year		227.0	2,013.0
Fiscal year before current fiscal year		2,017.0	2,390.0
Two years before current fiscal year		2,408.0	1,765.0
Three years before current fiscal year		1,751.0	1,404.0
Four years before current fiscal year		1,378.0	849.0
Prior		3,473.0	2,822.0
Revolving Loans Amortized Cost Basis		274.0	283.0
Total Loans and Leases		11,528.0	11,526.0
Current fiscal year, writeoff		0.0
Fiscal year before current fiscal year, writeoff		0.0
Two years before current fiscal year, writeoff		0.1
Three years before current fiscal year, writeoff		0.0
Four years before current fiscal year, writeoff		0.0
Prior, writeoff		6.4
Revolving Loans Amortized Cost Basis, writeoff		0.0
Total Loans and Leases, writeoff		6.5
Total commercial loans and leases | Commercial real estate | Current
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases		11,475.0	11,474.0
Total commercial loans and leases | Commercial real estate | Past due
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases		53.0	52.0
Total commercial loans and leases | Commercial real estate | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year		225.0	1,967.0
Fiscal year before current fiscal year		1,967.0	2,348.0
Two years before current fiscal year		2,368.0	1,678.0
Three years before current fiscal year		1,647.0	1,283.0
Four years before current fiscal year		1,270.0	700.0
Prior		2,984.0	2,447.0
Revolving Loans Amortized Cost Basis		245.0	258.0
Total Loans and Leases		10,706.0	10,681.0
Total commercial loans and leases | Commercial real estate | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year		2.0	43.0
Fiscal year before current fiscal year		44.0	35.0
Two years before current fiscal year		33.0	67.0
Three years before current fiscal year		84.0	74.0
Four years before current fiscal year		48.0	104.0
Prior		268.0	208.0
Revolving Loans Amortized Cost Basis		8.0	5.0
Total Loans and Leases		487.0	536.0
Total commercial loans and leases | Commercial real estate | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year		0.0	3.0
Fiscal year before current fiscal year		6.0	7.0
Two years before current fiscal year		7.0	20.0
Three years before current fiscal year		20.0	47.0
Four years before current fiscal year		60.0	45.0
Prior		221.0	167.0
Revolving Loans Amortized Cost Basis		21.0	20.0
Total Loans and Leases		335.0	309.0
Total commercial loans and leases | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year		370.0	1,655.0
Fiscal year before current fiscal year		1,614.0	1,249.0
Two years before current fiscal year		1,247.0	787.0
Three years before current fiscal year		765.0	568.0
Four years before current fiscal year		534.0	375.0
Prior		842.0	535.0
Revolving Loans Amortized Cost Basis		1,874.0	1,962.0
Total Loans and Leases		7,246.0	7,131.0
Current fiscal year, writeoff		0.0
Fiscal year before current fiscal year, writeoff		0.2
Two years before current fiscal year, writeoff		0.1
Three years before current fiscal year, writeoff		0.3
Four years before current fiscal year, writeoff		0.6
Prior, writeoff		4.6
Revolving Loans Amortized Cost Basis, writeoff		0.0
Total Loans and Leases, writeoff		5.8
Total commercial loans and leases | Commercial and industrial | Current
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases		7,198.0	7,077.0
Total commercial loans and leases | Commercial and industrial | Past due
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases		48.0	54.0
Total commercial loans and leases | Commercial and industrial | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year		359.0	1,635.0
Fiscal year before current fiscal year		1,576.0	1,194.0
Two years before current fiscal year		1,159.0	760.0
Three years before current fiscal year		747.0	533.0
Four years before current fiscal year		489.0	289.0
Prior		654.0	453.0
Revolving Loans Amortized Cost Basis		1,742.0	1,856.0
Total Loans and Leases		6,726.0	6,720.0
Total commercial loans and leases | Commercial and industrial | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year		4.0	15.0
Fiscal year before current fiscal year		26.0	43.0
Two years before current fiscal year		47.0	16.0
Three years before current fiscal year		10.0	27.0
Four years before current fiscal year		25.0	48.0
Prior		109.0	48.0
Revolving Loans Amortized Cost Basis		34.0	54.0
Total Loans and Leases		255.0	251.0
Total commercial loans and leases | Commercial and industrial | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year		7.0	5.0
Fiscal year before current fiscal year		12.0	12.0
Two years before current fiscal year		41.0	11.0
Three years before current fiscal year		8.0	8.0
Four years before current fiscal year		20.0	38.0
Prior		79.0	34.0
Revolving Loans Amortized Cost Basis		98.0	52.0
Total Loans and Leases		265.0	160.0
Total commercial loans and leases | Commercial leases
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year		112.0	189.0
Fiscal year before current fiscal year		146.0	127.0
Two years before current fiscal year		119.0	77.0
Three years before current fiscal year		74.0	61.0
Four years before current fiscal year		53.0	37.0
Prior		58.0	28.0
Revolving Loans Amortized Cost Basis		0.0	0.0
Total Loans and Leases		562.0	519.0
Current fiscal year, writeoff		0.0
Fiscal year before current fiscal year, writeoff		0.0
Two years before current fiscal year, writeoff		0.0
Three years before current fiscal year, writeoff		0.0
Four years before current fiscal year, writeoff		0.0
Prior, writeoff		0.0
Revolving Loans Amortized Cost Basis, writeoff		0.0
Total Loans and Leases, writeoff		0.0
Total commercial loans and leases | Commercial leases | Current
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases		560.0	515.0
Total commercial loans and leases | Commercial leases | Past due
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases		2.0	4.0
Total commercial loans and leases | Commercial leases | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year		105.0	187.0
Fiscal year before current fiscal year		142.0	121.0
Two years before current fiscal year		114.0	69.0
Three years before current fiscal year		66.0	59.0
Four years before current fiscal year		51.0	36.0
Prior		57.0	27.0
Revolving Loans Amortized Cost Basis		0.0	0.0
Total Loans and Leases		535.0	499.0
Total commercial loans and leases | Commercial leases | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year		7.0	0.0
Fiscal year before current fiscal year		2.0	1.0
Two years before current fiscal year		1.0	0.0
Three years before current fiscal year		0.0	1.0
Four years before current fiscal year		0.0	0.0
Prior		0.0	0.0
Revolving Loans Amortized Cost Basis		0.0	0.0
Total Loans and Leases		10.0	2.0
Total commercial loans and leases | Commercial leases | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year		0.0	2.0
Fiscal year before current fiscal year		2.0	5.0
Two years before current fiscal year		4.0	8.0
Three years before current fiscal year		8.0	1.0
Four years before current fiscal year		2.0	1.0
Prior		1.0	1.0
Revolving Loans Amortized Cost Basis		0.0	0.0
Total Loans and Leases		17.0	18.0
Total commercial loans and leases | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year		57.0	58.0
Fiscal year before current fiscal year		0.0	0.0
Two years before current fiscal year		0.0	0.0
Three years before current fiscal year		0.0	0.0
Four years before current fiscal year		0.0	0.0
Prior		11.0	12.0
Revolving Loans Amortized Cost Basis		108.0	44.0
Total Loans and Leases		176.0	114.0
Current fiscal year, writeoff		0.0
Fiscal year before current fiscal year, writeoff		0.0
Two years before current fiscal year, writeoff		0.0
Three years before current fiscal year, writeoff		0.0
Four years before current fiscal year, writeoff		0.0
Prior, writeoff		0.8
Revolving Loans Amortized Cost Basis, writeoff		0.0
Total Loans and Leases, writeoff		0.8
Total commercial loans and leases | Other | Current
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases		176.0	113.0
Total commercial loans and leases | Other | Past due
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases		0.0	1.0
Total commercial loans and leases | Other | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year		57.0	58.0
Fiscal year before current fiscal year		0.0	0.0
Two years before current fiscal year		0.0	0.0
Three years before current fiscal year		0.0	0.0
Four years before current fiscal year		0.0	0.0
Prior		11.0	12.0
Revolving Loans Amortized Cost Basis		108.0	44.0
Total Loans and Leases		176.0	114.0
Total consumer loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year		461.0	3,146.0
Fiscal year before current fiscal year		3,161.0	2,864.0
Two years before current fiscal year		2,800.0	1,499.0
Three years before current fiscal year		1,446.0	636.0
Four years before current fiscal year		608.0	310.0
Prior		1,636.0	1,419.0
Revolving Loans Amortized Cost Basis		1,049.0	1,091.0
Total Loans and Leases		11,161.0	10,965.0
Total consumer loans | Current
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases		11,081.0	10,860.0
Total consumer loans | Past due
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases		80.0	105.0
Total consumer loans | Direct installment
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year		63.0	801.0
Fiscal year before current fiscal year		782.0	888.0
Two years before current fiscal year		864.0	454.0
Three years before current fiscal year		437.0	164.0
Four years before current fiscal year		157.0	92.0
Prior		449.0	385.0
Revolving Loans Amortized Cost Basis		0.0	0.0
Total Loans and Leases		2,752.0	2,784.0
Current fiscal year, writeoff		0.0
Fiscal year before current fiscal year, writeoff		0.0
Two years before current fiscal year, writeoff		0.1
Three years before current fiscal year, writeoff		0.0
Four years before current fiscal year, writeoff		0.0
Prior, writeoff		0.2
Revolving Loans Amortized Cost Basis, writeoff		0.0
Total Loans and Leases, writeoff		0.3
Total consumer loans | Direct installment | Current
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year		63.0	801.0
Fiscal year before current fiscal year		781.0	887.0
Two years before current fiscal year		863.0	453.0
Three years before current fiscal year		437.0	163.0
Four years before current fiscal year		157.0	91.0
Prior		439.0	374.0
Revolving Loans Amortized Cost Basis		0.0	0.0
Total Loans and Leases		2,740.0	2,769.0
Total consumer loans | Direct installment | Past due
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year		0.0	0.0
Fiscal year before current fiscal year		1.0	1.0
Two years before current fiscal year		1.0	1.0
Three years before current fiscal year		0.0	1.0
Four years before current fiscal year		0.0	1.0
Prior		10.0	11.0
Revolving Loans Amortized Cost Basis		0.0	0.0
Total Loans and Leases		12.0	15.0
Total consumer loans | Residential mortgages
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year		269.0	1,466.0
Fiscal year before current fiscal year		1,557.0	1,590.0
Two years before current fiscal year		1,584.0	874.0
Three years before current fiscal year		856.0	380.0
Four years before current fiscal year		372.0	133.0
Prior		950.0	852.0
Revolving Loans Amortized Cost Basis		1.0	2.0
Total Loans and Leases		5,589.0	5,297.0
Current fiscal year, writeoff		0.0
Fiscal year before current fiscal year, writeoff		0.0
Two years before current fiscal year, writeoff		0.0
Three years before current fiscal year, writeoff		0.0
Four years before current fiscal year, writeoff		0.0
Prior, writeoff		0.4
Revolving Loans Amortized Cost Basis, writeoff		0.0
Total Loans and Leases, writeoff		0.4
Total consumer loans | Residential mortgages | Current
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year		269.0	1,464.0
Fiscal year before current fiscal year		1,555.0	1,587.0
Two years before current fiscal year		1,582.0	871.0
Three years before current fiscal year		853.0	378.0
Four years before current fiscal year		371.0	128.0
Prior		919.0	819.0
Revolving Loans Amortized Cost Basis		1.0	2.0
Total Loans and Leases		5,550.0	5,249.0
Total consumer loans | Residential mortgages | Past due
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year		0.0	2.0
Fiscal year before current fiscal year		2.0	3.0
Two years before current fiscal year		2.0	3.0
Three years before current fiscal year		3.0	2.0
Four years before current fiscal year		1.0	5.0
Prior		31.0	33.0
Revolving Loans Amortized Cost Basis		0.0	0.0
Total Loans and Leases		39.0	48.0
Total consumer loans | Indirect installment
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year		117.0	805.0
Fiscal year before current fiscal year		750.0	368.0
Two years before current fiscal year		335.0	169.0
Three years before current fiscal year		151.0	89.0
Four years before current fiscal year		76.0	81.0
Prior		96.0	41.0
Revolving Loans Amortized Cost Basis		0.0	0.0
Total Loans and Leases		1,525.0	1,553.0
Current fiscal year, writeoff		0.0
Fiscal year before current fiscal year, writeoff		1.0
Two years before current fiscal year, writeoff		1.2
Three years before current fiscal year, writeoff		0.2
Four years before current fiscal year, writeoff		0.0
Prior, writeoff		0.2
Revolving Loans Amortized Cost Basis, writeoff		0.0
Total Loans and Leases, writeoff		2.6
Total consumer loans | Indirect installment | Current
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year		117.0	800.0
Fiscal year before current fiscal year		746.0	357.0
Two years before current fiscal year		329.0	166.0
Three years before current fiscal year		149.0	88.0
Four years before current fiscal year		75.0	80.0
Prior		95.0	40.0
Revolving Loans Amortized Cost Basis		0.0	0.0
Total Loans and Leases		1,511.0	1,531.0
Total consumer loans | Indirect installment | Past due
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year		0.0	5.0
Fiscal year before current fiscal year		4.0	11.0
Two years before current fiscal year		6.0	3.0
Three years before current fiscal year		2.0	1.0
Four years before current fiscal year		1.0	1.0
Prior		1.0	1.0
Revolving Loans Amortized Cost Basis		0.0	0.0
Total Loans and Leases		14.0	22.0
Total consumer loans | Consumer lines of credit
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year		12.0	74.0
Fiscal year before current fiscal year		72.0	18.0
Two years before current fiscal year		17.0	2.0
Three years before current fiscal year		2.0	3.0
Four years before current fiscal year		3.0	4.0
Prior		141.0	141.0
Revolving Loans Amortized Cost Basis		1,048.0	1,089.0
Total Loans and Leases		1,295.0	1,331.0
Current fiscal year, writeoff		0.0
Fiscal year before current fiscal year, writeoff		0.0
Two years before current fiscal year, writeoff		0.0
Three years before current fiscal year, writeoff		0.0
Four years before current fiscal year, writeoff		0.0
Prior, writeoff		0.3
Revolving Loans Amortized Cost Basis, writeoff		0.0
Total Loans and Leases, writeoff		0.3
Total consumer loans | Consumer lines of credit | Current
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year		12.0	74.0
Fiscal year before current fiscal year		72.0	17.0
Two years before current fiscal year		17.0	1.0
Three years before current fiscal year		2.0	3.0
Four years before current fiscal year		3.0	4.0
Prior		128.0	126.0
Revolving Loans Amortized Cost Basis		1,046.0	1,086.0
Total Loans and Leases		1,280.0	1,311.0
Total consumer loans | Consumer lines of credit | Past due
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year		0.0	0.0
Fiscal year before current fiscal year		0.0	1.0
Two years before current fiscal year		0.0	1.0
Three years before current fiscal year		0.0	0.0
Four years before current fiscal year		0.0	0.0
Prior		13.0	15.0
Revolving Loans Amortized Cost Basis		2.0	3.0
Total Loans and Leases		$ 15.0	$ 20.0

[1] Amount represents loans for which we have elected the fair value option. See Note 19.