GUARANTEES, LEASES AND COMMITMENTS - Guarantees (Details)	Sep. 30, 2020 USD ($) trust	Dec. 31, 2019 USD ($)
Maximum potential amount of future payments
Expire within 1 year	$ 249,700,000,000	$ 253,600,000,000
Expire after 1 year	164,200,000,000	163,000,000,000.0
Total amount outstanding	413,900,000,000	416,600,000,000
Carrying value	$ 2,271,000,000	1,162,000,000
Number of trusts funded by the reinsurer | trust	2
Liability related to long-term care insurance indemnification	$ 0	0
Cash collateral available to reimburse losses realized under guarantees and indemnifications	47,500,000,000	46,700,000,000
Securities and other marketable assets held as collateral	72,000,000,000.0	58,600,000,000
Letters of credit in favor of the Company held as collateral	6,500,000,000	4,400,000,000
Financial standby letters of credit
Maximum potential amount of future payments
Expire within 1 year	23,800,000,000	31,900,000,000
Expire after 1 year	67,700,000,000	61,400,000,000
Total amount outstanding	91,500,000,000	93,300,000,000
Carrying value	1,201,000,000	581,000,000
Performance guarantees
Maximum potential amount of future payments
Expire within 1 year	7,100,000,000	6,900,000,000
Expire after 1 year	5,800,000,000	5,500,000,000
Total amount outstanding	12,900,000,000	12,400,000,000
Carrying value	88,000,000	36,000,000
Derivative instruments deemed to be guarantees
Maximum potential amount of future payments
Expire within 1 year	20,200,000,000	35,200,000,000
Expire after 1 year	53,700,000,000	60,800,000,000
Total amount outstanding	73,900,000,000	96,000,000,000.0
Carrying value	925,000,000	474,000,000
Loans sold with recourse
Maximum potential amount of future payments
Expire within 1 year	0	0
Expire after 1 year	1,200,000,000	1,200,000,000
Total amount outstanding	1,200,000,000	1,200,000,000
Carrying value	6,000,000	7,000,000
Repurchase reserve for consumer mortgages representations and warranties	33,000,000	37,000,000
Securities lending indemnifications
Maximum potential amount of future payments
Expire within 1 year	102,000,000,000.0	87,800,000,000
Expire after 1 year	0	0
Total amount outstanding	102,000,000,000.0	87,800,000,000
Carrying value	0	0
Credit card merchant processing
Maximum potential amount of future payments
Expire within 1 year	96,600,000,000	91,600,000,000
Expire after 1 year	0	0
Total amount outstanding	96,600,000,000	91,600,000,000
Carrying value	4,000,000	0
Credit card arrangements with partners
Maximum potential amount of future payments
Expire within 1 year	0	200,000,000
Expire after 1 year	1,100,000,000	400,000,000
Total amount outstanding	1,100,000,000	600,000,000
Carrying value	7,000,000	23,000,000
Custody indemnifications and other
Maximum potential amount of future payments
Expire within 1 year	0	0
Expire after 1 year	34,700,000,000	33,700,000,000
Total amount outstanding	34,700,000,000	33,700,000,000
Carrying value	40,000,000	41,000,000
Futures and over-the-counter derivatives clearing
Maximum potential amount of future payments
Amount of cash initial margin collected and remitted	$ 16,400,000,000	$ 13,300,000,000