GUARANTEES AND COMMITMENTS - Guarantees (Details)	Sep. 30, 2018 USD ($) trust	Dec. 31, 2017 USD ($) trust
Maximum potential amount of future payments
Expire within 1 year	$ 274,900,000,000	$ 235,600,000,000
Expire after 1 year	195,100,000,000	193,400,000,000
Total amount outstanding	470,000,000,000	429,000,000,000
Carrying value	$ 735,000,000	$ 809,000,000
Number of trusts funded by the reinsurer | trust	2	2
Fair value of securities in trusts funded by reinsurer relating to indemnification	$ 7,400,000,000	$ 7,500,000,000
Liability related to long-term care insurance indemnification	0	0
Cash collateral available to reimburse losses realized under guarantees and indemnifications	51,000,000,000	46,000,000,000
Securities and other marketable assets held as collateral	82,000,000,000	70,000,000,000
Letters of credit in favor of the Company held as collateral	3,900,000,000	3,700,000,000
Financial standby letters of credit
Maximum potential amount of future payments
Expire within 1 year	29,900,000,000	27,900,000,000
Expire after 1 year	65,500,000,000	65,900,000,000
Total amount outstanding	95,400,000,000	93,800,000,000
Carrying value	165,000,000	93,000,000
Performance guarantees
Maximum potential amount of future payments
Expire within 1 year	7,800,000,000	7,200,000,000
Expire after 1 year	4,000,000,000	4,100,000,000
Total amount outstanding	11,800,000,000	11,300,000,000
Carrying value	30,000,000	20,000,000
Derivative instruments deemed to be guarantees
Maximum potential amount of future payments
Expire within 1 year	21,200,000,000	11,000,000,000
Expire after 1 year	84,500,000,000	84,900,000,000
Total amount outstanding	105,700,000,000	95,900,000,000
Carrying value	307,000,000	423,000,000
Loans sold with recourse
Maximum potential amount of future payments
Expire within 1 year	0	0
Expire after 1 year	1,400,000,000	1,400,000,000
Total amount outstanding	1,400,000,000	1,400,000,000
Carrying value	9,000,000	9,000,000
Repurchase reserve for Consumer mortgages representations and warranties	54,000,000	66,000,000
Securities lending indemnifications
Maximum potential amount of future payments
Expire within 1 year	120,500,000,000	103,700,000,000
Expire after 1 year	0	0
Total amount outstanding	120,500,000,000	103,700,000,000
Carrying value	0	0
Credit card merchant processing
Maximum potential amount of future payments
Expire within 1 year	95,500,000,000	85,500,000,000
Expire after 1 year	0	0
Total amount outstanding	95,500,000,000	85,500,000,000
Carrying value	0	0
Credit card arrangements with partners
Maximum potential amount of future payments
Expire within 1 year	0	300,000,000
Expire after 1 year	1,100,000,000	1,100,000,000
Total amount outstanding	1,100,000,000	1,400,000,000
Carrying value	162,000,000	205,000,000
Custody indemnifications and other
Maximum potential amount of future payments
Expire within 1 year	0	0
Expire after 1 year	38,600,000,000	36,000,000,000
Total amount outstanding	38,600,000,000	36,000,000,000
Carrying value	62,000,000	59,000,000
Futures and over-the-counter derivatives clearing
Maximum potential amount of future payments
Amount of cash initial margin collected and remitted	$ 13,200,000,000	$ 10,700,000,000