GUARANTEES AND COMMITMENTS - Guarantees (Details)	Jun. 30, 2018 USD ($) trust	Dec. 31, 2017 USD ($) trust
Maximum potential amount of future payments
Expire within 1 year	$ 269,100,000,000	$ 235,600,000,000
Expire after 1 year	191,000,000,000	192,200,000,000
Total amount outstanding	460,100,000,000	427,800,000,000
Carrying value	$ 873,000,000	$ 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	85,000,000,000	70,000,000,000
Letters of credit in favor of the Company held as collateral	3,800,000,000	3,700,000,000
Financial standby letters of credit
Maximum potential amount of future payments
Expire within 1 year	30,100,000,000	27,900,000,000
Expire after 1 year	64,200,000,000	65,900,000,000
Total amount outstanding	94,300,000,000	93,800,000,000
Carrying value	149,000,000	93,000,000
Performance guarantees
Maximum potential amount of future payments
Expire within 1 year	7,700,000,000	7,200,000,000
Expire after 1 year	4,200,000,000	4,100,000,000
Total amount outstanding	11,900,000,000	11,300,000,000
Carrying value	29,000,000	20,000,000
Derivative instruments deemed to be guarantees
Maximum potential amount of future payments
Expire within 1 year	15,500,000,000	11,000,000,000
Expire after 1 year	84,100,000,000	84,900,000,000
Total amount outstanding	99,600,000,000	95,900,000,000
Carrying value	396,000,000	423,000,000
Loans sold with recourse
Maximum potential amount of future payments
Expire within 1 year	0	0
Expire after 1 year	300,000,000	200,000,000
Total amount outstanding	300,000,000	200,000,000
Carrying value	9,000,000	9,000,000
Repurchase reserve for Consumer mortgages representations and warranties	56,000,000	66,000,000
Securities lending indemnifications
Maximum potential amount of future payments
Expire within 1 year	121,500,000,000	103,700,000,000
Expire after 1 year	0	0
Total amount outstanding	121,500,000,000	103,700,000,000
Carrying value	0	0
Credit card merchant processing
Maximum potential amount of future payments
Expire within 1 year	94,200,000,000	85,500,000,000
Expire after 1 year	0	0
Total amount outstanding	94,200,000,000	85,500,000,000
Carrying value	0	0
Credit card arrangements with partners
Maximum potential amount of future payments
Expire within 1 year	100,000,000	300,000,000
Expire after 1 year	1,100,000,000	1,100,000,000
Total amount outstanding	1,200,000,000	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	37,100,000,000	36,000,000,000
Total amount outstanding	37,100,000,000	36,000,000,000
Carrying value	128,000,000	59,000,000
Futures and over-the-counter derivatives clearing
Maximum potential amount of future payments
Amount of cash initial margin collected and remitted	$ 12,500,000,000	$ 10,700,000,000