GUARANTEES AND COMMITMENTS - Guarantees (Details)	Mar. 31, 2018 USD ($) trust	Dec. 31, 2017 USD ($) trust
Maximum potential amount of future payments
Expire within 1 year	$ 264,500,000,000	$ 235,600,000,000
Expire after 1 year	192,500,000,000	192,200,000,000
Total amount outstanding	457,000,000,000	427,800,000,000
Carrying value	$ 846,000,000	$ 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	52,000,000,000	46,000,000,000
Securities and other marketable assets held as collateral	88,000,000,000	70,000,000,000
Letters of credit in favor of the Company held as collateral	3,900,000,000	3,700,000,000
Investment grade
Maximum potential amount of future payments
Total amount outstanding	102,100,000,000	99,700,000,000
Non-investment grade
Maximum potential amount of future payments
Total amount outstanding	25,300,000,000	25,600,000,000
Not rated
Maximum potential amount of future payments
Total amount outstanding	329,600,000,000	302,500,000,000
Financial standby letters of credit
Maximum potential amount of future payments
Expire within 1 year	30,400,000,000	27,900,000,000
Expire after 1 year	63,000,000,000	65,900,000,000
Total amount outstanding	93,400,000,000	93,800,000,000
Carrying value	131,000,000	93,000,000
Financial standby letters of credit | Investment grade
Maximum potential amount of future payments
Total amount outstanding	68,100,000,000	68,100,000,000
Financial standby letters of credit | Non-investment grade
Maximum potential amount of future payments
Total amount outstanding	10,300,000,000	10,900,000,000
Financial standby letters of credit | Not rated
Maximum potential amount of future payments
Total amount outstanding	15,000,000,000	14,800,000,000
Performance guarantees
Maximum potential amount of future payments
Expire within 1 year	7,500,000,000	7,200,000,000
Expire after 1 year	4,100,000,000	4,100,000,000
Total amount outstanding	11,600,000,000	11,300,000,000
Carrying value	31,000,000	20,000,000
Performance guarantees | Investment grade
Maximum potential amount of future payments
Total amount outstanding	8,200,000,000	7,900,000,000
Performance guarantees | Non-investment grade
Maximum potential amount of future payments
Total amount outstanding	2,300,000,000	2,400,000,000
Performance guarantees | Not rated
Maximum potential amount of future payments
Total amount outstanding	1,100,000,000	1,000,000,000
Derivative instruments deemed to be guarantees
Maximum potential amount of future payments
Expire within 1 year	17,000,000,000	11,000,000,000
Expire after 1 year	85,600,000,000	84,900,000,000
Total amount outstanding	102,600,000,000	95,900,000,000
Carrying value	432,000,000	423,000,000
Derivative instruments deemed to be guarantees | Investment grade
Maximum potential amount of future payments
Total amount outstanding	0	0
Derivative instruments deemed to be guarantees | Non-investment grade
Maximum potential amount of future payments
Total amount outstanding	0	0
Derivative instruments deemed to be guarantees | Not rated
Maximum potential amount of future payments
Total amount outstanding	102,600,000,000	95,900,000,000
Loans sold with recourse
Maximum potential amount of future payments
Expire within 1 year	0	0
Expire after 1 year	200,000,000	200,000,000
Total amount outstanding	200,000,000	200,000,000
Carrying value	8,000,000	9,000,000
Repurchase reserve for Consumer mortgages representations and warranties	66,000,000	66,000,000
Loans sold with recourse | Investment grade
Maximum potential amount of future payments
Total amount outstanding	0	0
Loans sold with recourse | Non-investment grade
Maximum potential amount of future payments
Total amount outstanding	0	0
Loans sold with recourse | Not rated
Maximum potential amount of future payments
Total amount outstanding	200,000,000	200,000,000
Securities lending indemnifications
Maximum potential amount of future payments
Expire within 1 year	126,900,000,000	103,700,000,000
Expire after 1 year	0	0
Total amount outstanding	126,900,000,000	103,700,000,000
Carrying value	0	0
Securities lending indemnifications | Investment grade
Maximum potential amount of future payments
Total amount outstanding	0	0
Securities lending indemnifications | Non-investment grade
Maximum potential amount of future payments
Total amount outstanding	0	0
Securities lending indemnifications | Not rated
Maximum potential amount of future payments
Total amount outstanding	126,900,000,000	103,700,000,000
Credit card merchant processing
Maximum potential amount of future payments
Expire within 1 year	82,500,000,000	85,500,000,000
Expire after 1 year	0	0
Total amount outstanding	82,500,000,000	85,500,000,000
Carrying value	0	0
Credit card merchant processing | Investment grade
Maximum potential amount of future payments
Total amount outstanding	0	0
Credit card merchant processing | Non-investment grade
Maximum potential amount of future payments
Total amount outstanding	0	0
Credit card merchant processing | Not rated
Maximum potential amount of future payments
Total amount outstanding	82,500,000,000	85,500,000,000
Credit card arrangements with partners
Maximum potential amount of future payments
Expire within 1 year	200,000,000	300,000,000
Expire after 1 year	1,100,000,000	1,100,000,000
Total amount outstanding	1,300,000,000	1,400,000,000
Carrying value	162,000,000	205,000,000
Credit card arrangements with partners | Investment grade
Maximum potential amount of future payments
Total amount outstanding	0	0
Credit card arrangements with partners | Non-investment grade
Maximum potential amount of future payments
Total amount outstanding	0	0
Credit card arrangements with partners | Not rated
Maximum potential amount of future payments
Total amount outstanding	1,300,000,000	1,400,000,000
Custody indemnifications and other
Maximum potential amount of future payments
Expire within 1 year	0	0
Expire after 1 year	38,500,000,000	36,000,000,000
Total amount outstanding	38,500,000,000	36,000,000,000
Carrying value	82,000,000	59,000,000
Custody indemnifications and other | Investment grade
Maximum potential amount of future payments
Total amount outstanding	25,800,000,000	23,700,000,000
Custody indemnifications and other | Non-investment grade
Maximum potential amount of future payments
Total amount outstanding	12,700,000,000	12,300,000,000
Custody indemnifications and other | Not rated
Maximum potential amount of future payments
Total amount outstanding	0	0
Futures and over-the-counter derivatives clearing
Maximum potential amount of future payments
Amount of cash initial margin collected and remitted	$ 11,600,000,000	$ 10,700,000,000