GUARANTEES, LEASES AND COMMITMENTS - Guarantees (Details)	Sep. 30, 2021 USD ($) trust	Dec. 31, 2020 USD ($)
Maximum potential amount of future payments
Expire within 1 year	$ 297,400,000,000	$ 266,900,000,000
Expire after 1 year	152,900,000,000	174,600,000,000
Total amount outstanding	450,300,000,000	441,500,000,000
Carrying value	$ 1,403,000,000	2,204,000,000
Number of trusts funded by the reinsurer | trust	2
Liability related to long-term care insurance indemnification	$ 0	0
Amount of cash initial margin collected and remitted	17,100,000,000	16,600,000,000
Cash collateral available to reimburse losses realized under guarantees and indemnifications	62,800,000,000	51,600,000,000
Securities and other marketable assets held as collateral	88,100,000,000	80,100,000,000
Letters of credit in favor of the Company held as collateral	3,900,000,000	6,600,000,000
Financial standby letters of credit
Maximum potential amount of future payments
Expire within 1 year	27,600,000,000	25,300,000,000
Expire after 1 year	64,900,000,000	68,400,000,000
Total amount outstanding	92,500,000,000	93,700,000,000
Carrying value	937,000,000	1,407,000,000
Performance guarantees
Maximum potential amount of future payments
Expire within 1 year	6,500,000,000	7,300,000,000
Expire after 1 year	6,100,000,000	6,000,000,000.0
Total amount outstanding	12,600,000,000	13,300,000,000
Carrying value	46,000,000	72,000,000
Derivative instruments considered to be guarantees
Maximum potential amount of future payments
Expire within 1 year	17,000,000,000.0	20,000,000,000.0
Expire after 1 year	54,900,000,000	60,900,000,000
Total amount outstanding	71,900,000,000	80,900,000,000
Carrying value	360,000,000	671,000,000
Loans sold with recourse
Maximum potential amount of future payments
Expire within 1 year	0	0
Expire after 1 year	1,700,000,000	1,200,000,000
Total amount outstanding	1,700,000,000	1,200,000,000
Carrying value	15,000,000	9,000,000
Repurchase reserve for consumer mortgages representations and warranties	32,000,000	31,000,000
Securities lending indemnifications
Maximum potential amount of future payments
Expire within 1 year	131,700,000,000	112,200,000,000
Expire after 1 year	0	0
Total amount outstanding	131,700,000,000	112,200,000,000
Carrying value	0	0
Credit card merchant processing
Maximum potential amount of future payments
Expire within 1 year	114,600,000,000	101,900,000,000
Expire after 1 year	0	0
Total amount outstanding	114,600,000,000	101,900,000,000
Carrying value	1,000,000	3,000,000
Credit card arrangements with partners
Maximum potential amount of future payments
Expire within 1 year	0	200,000,000
Expire after 1 year	800,000,000	800,000,000
Total amount outstanding	800,000,000	1,000,000,000.0
Carrying value	7,000,000	7,000,000
Custody indemnifications and other
Maximum potential amount of future payments
Expire within 1 year	0	0
Expire after 1 year	24,500,000,000	37,300,000,000
Total amount outstanding	24,500,000,000	37,300,000,000
Carrying value	$ 37,000,000	$ 35,000,000