PLEDGED ASSETS, COLLATERAL, GUARANTEES AND COMMITMENTS - Guarantees (Details)	12 Months Ended
	Dec. 31, 2017 USD ($) margin	Dec. 31, 2016 USD ($)	Dec. 31, 2000 trust
Maximum potential amount of future payments
Expire Within One Year	$ 235,600,000,000	$ 207,400,000,000
Expire After One Year	192,200,000,000	197,800,000,000
Total amount outstanding	427,800,000,000	405,200,000,000
Carrying value	809,000,000	1,183,000,000
Compensation for standard representations and warranties	0
Stated or notional amounts included in the indemnification clauses	0
Number of trusts funded by the reinsurer | trust			2
Fair value of securities in trusts funded by reinsurer relating to indemnification	7,500,000,000	7,000,000,000
Liability related to long-term care insurance indemnification	0	0
Cash collateral available to reimburse losses realized under guarantees and indemnifications	46,000,000,000	48,000,000,000
Available-for-sale securities, pledged to creditors	70,000,000,000	41,000,000,000
Letters of credit in favor of the Company held as collateral	3,700,000,000	5,400,000,000
Investment Grade
Maximum potential amount of future payments
Total amount outstanding	99,700,000,000	106,400,000,000
Non-Investment Grade
Maximum potential amount of future payments
Total amount outstanding	25,600,000,000	29,500,000,000
Not rated
Maximum potential amount of future payments
Total amount outstanding	302,500,000,000	269,300,000,000
Financial standby letters of credit
Maximum potential amount of future payments
Expire Within One Year	27,900,000,000	26,000,000,000
Expire After One Year	65,900,000,000	67,100,000,000
Total amount outstanding	93,800,000,000	93,100,000,000
Carrying value	93,000,000	141,000,000
Financial standby letters of credit | Investment Grade
Maximum potential amount of future payments
Total amount outstanding	68,100,000,000	66,800,000,000
Financial standby letters of credit | Non-Investment Grade
Maximum potential amount of future payments
Total amount outstanding	10,900,000,000	13,400,000,000
Financial standby letters of credit | Not rated
Maximum potential amount of future payments
Total amount outstanding	14,800,000,000	12,900,000,000
Performance guarantees
Maximum potential amount of future payments
Expire Within One Year	7,200,000,000	7,500,000,000
Expire After One Year	4,100,000,000	3,600,000,000
Total amount outstanding	11,300,000,000	11,100,000,000
Carrying value	20,000,000	19,000,000
Performance guarantees | Investment Grade
Maximum potential amount of future payments
Total amount outstanding	7,900,000,000	6,300,000,000
Performance guarantees | Non-Investment Grade
Maximum potential amount of future payments
Total amount outstanding	2,400,000,000	4,000,000,000
Performance guarantees | Not rated
Maximum potential amount of future payments
Total amount outstanding	1,000,000,000	800,000,000
Derivative instruments considered to be guarantees
Maximum potential amount of future payments
Expire Within One Year	11,000,000,000	7,200,000,000
Expire After One Year	84,900,000,000	80,000,000,000
Total amount outstanding	95,900,000,000	87,200,000,000
Carrying value	423,000,000	747,000,000
Derivative instruments considered to be guarantees | Investment Grade
Maximum potential amount of future payments
Total amount outstanding	0	0
Derivative instruments considered to be guarantees | Non-Investment Grade
Maximum potential amount of future payments
Total amount outstanding	0	0
Derivative instruments considered to be guarantees | Not rated
Maximum potential amount of future payments
Total amount outstanding	95,900,000,000	87,200,000,000
Loans sold with recourse
Maximum potential amount of future payments
Expire Within One Year	0	0
Expire After One Year	200,000,000	200,000,000
Total amount outstanding	200,000,000	200,000,000
Carrying value	9,000,000	12,000,000
Repurchase reserve for Consumer mortgages representations and warranties	66,000,000	107,000,000
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 One Year	103,700,000,000	80,300,000,000
Expire After One Year	0	0
Total amount outstanding	103,700,000,000	80,300,000,000
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	103,700,000,000	80,300,000,000
Credit card merchant processing
Maximum potential amount of future payments
Expire Within One Year	85,500,000,000	86,400,000,000
Expire After One Year	0	0
Total amount outstanding	85,500,000,000	86,400,000,000
Carrying value	0	0
Maximum potential contingent liability related to bankcard and private-label merchant processing services	86,000,000,000	86,000,000,000
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	85,500,000,000	86,400,000,000
Credit card arrangements with partners
Maximum potential amount of future payments
Expire Within One Year	300,000,000	0
Expire After One Year	1,100,000,000	1,500,000,000
Total amount outstanding	1,400,000,000	1,500,000,000
Carrying value	205,000,000	206,000,000
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	1,400,000,000	1,500,000,000
Custody indemnifications and other
Maximum potential amount of future payments
Expire Within One Year	0	0
Expire After One Year	36,000,000,000	45,400,000,000
Total amount outstanding	36,000,000,000	45,400,000,000
Carrying value	59,000,000	58,000,000
Custody indemnifications and other | Investment Grade
Maximum potential amount of future payments
Total amount outstanding	23,700,000,000	33,300,000,000
Custody indemnifications and other | Non-Investment Grade
Maximum potential amount of future payments
Total amount outstanding	12,300,000,000	12,100,000,000
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
Number of types of margin | margin	2
Amount of cash initial margin collected and remitted	$ 10,700,000,000	$ 9,400,000,000