BORROWINGS - Additional Information (Detail) - USD ($)	3 Months Ended	6 Months Ended
	Mar. 31, 2020	Jun. 30, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Short-term advances		$ 1,800,000,000	$ 1,500,000,000
Short-term advances, percentage bearing fixed interest rate		89.80%	64.50%
Long-term borrowings, face amount		$ 558,000,000
Proceeds from debt, net of issuance costs		560,000,000
FHLB [Member]
Debt Instrument [Line Items]
Credit available with FHLB		8,200,000,000
Credit with FHLB utilized		$ 2,900,000,000
Minimum [Member] | FHLB [Member]
Debt Instrument [Line Items]
Effective interest rates		0.33%	1.62%
Maximum [Member] | FHLB [Member]
Debt Instrument [Line Items]
Effective interest rates		2.71%	2.71%
2.20% Senior Notes due February 24, 2023 [Member]
Debt Instrument [Line Items]
Long-term borrowings, face amount	$ 300,000,000	$ 300,000,000
Proceeds from debt, net of issuance costs	$ 297,900,000	$ 298,000,000
London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Basis spread on variable rate		2.40%