PLEDGED ASSETS, COLLATERAL, GUARANTEES AND COMMITMENTS - Guarantees (Details)	12 Months Ended
	Dec. 31, 2018 USD ($) margin	Dec. 31, 2017 USD ($)	Dec. 31, 2000 trust
Maximum potential amount of future payments
Expire Within One Year	$ 256,600,000,000	$ 235,600,000,000
Expire After One Year	194,300,000,000	193,400,000,000
Total amount outstanding	450,900,000,000	429,000,000,000
Carrying value	939,000,000	809,000,000
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	7,500,000,000
Liability related to long-term care insurance indemnification	0	0
Cash collateral available to reimburse losses realized under guarantees and indemnifications	55,000,000,000	46,000,000,000
Available-for-sale securities, pledged to creditors	55,000,000,000	70,000,000,000
Letters of credit in favor of the Company held as collateral	4,100,000,000	3,700,000,000
Financial standby letters of credit
Maximum potential amount of future payments
Expire Within One Year	31,800,000,000	27,900,000,000
Expire After One Year	65,300,000,000	65,900,000,000
Total amount outstanding	97,100,000,000	93,800,000,000
Carrying value	131,000,000	93,000,000
Performance guarantees
Maximum potential amount of future payments
Expire Within One Year	7,700,000,000	7,200,000,000
Expire After One 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 considered to be guarantees
Maximum potential amount of future payments
Expire Within One Year	23,500,000,000	11,000,000,000
Expire After One Year	87,400,000,000	84,900,000,000
Total amount outstanding	110,900,000,000	95,900,000,000
Carrying value	567,000,000	423,000,000
Loans sold with recourse
Maximum potential amount of future payments
Expire Within One Year	0	0
Expire After One Year	1,200,000,000	1,400,000,000
Total amount outstanding	1,200,000,000	1,400,000,000
Carrying value	9,000,000	9,000,000
Repurchase reserve for Consumer mortgages representations and warranties	49,000,000	66,000,000
Securities lending indemnifications
Maximum potential amount of future payments
Expire Within One Year	98,300,000,000	103,700,000,000
Expire After One Year	0	0
Total amount outstanding	98,300,000,000	103,700,000,000
Carrying value	0	0
Credit card merchant processing
Maximum potential amount of future payments
Expire Within One Year	95,000,000,000	85,500,000,000
Expire After One Year	0	0
Total amount outstanding	95,000,000,000	85,500,000,000
Carrying value	0	0
Maximum potential contingent liability related to bankcard and private-label merchant processing services	95,000,000,000	86,000,000,000
Credit card arrangements with partners
Maximum potential amount of future payments
Expire Within One Year	300,000,000	300,000,000
Expire After One Year	800,000,000	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 One Year	0	0
Expire After One Year	35,400,000,000	36,000,000,000
Total amount outstanding	35,400,000,000	36,000,000,000
Carrying value	$ 41,000,000	59,000,000
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	$ 13,800,000,000	10,700,000,000
Investment Grade
Maximum potential amount of future payments
Total amount outstanding	99,700,000,000	99,700,000,000
Investment Grade | Financial standby letters of credit
Maximum potential amount of future payments
Total amount outstanding	68,300,000,000	68,100,000,000
Investment Grade | Performance guarantees
Maximum potential amount of future payments
Total amount outstanding	9,200,000,000	7,900,000,000
Investment Grade | Derivative instruments considered to be guarantees
Maximum potential amount of future payments
Total amount outstanding	0	0
Investment Grade | Loans sold with recourse
Maximum potential amount of future payments
Total amount outstanding	0	0
Investment Grade | Securities lending indemnifications
Maximum potential amount of future payments
Total amount outstanding	0	0
Investment Grade | Credit card merchant processing
Maximum potential amount of future payments
Total amount outstanding	0	0
Investment Grade | Credit card arrangements with partners
Maximum potential amount of future payments
Total amount outstanding	0	0
Investment Grade | Custody indemnifications and other
Maximum potential amount of future payments
Total amount outstanding	22,200,000,000	23,700,000,000
Non-Investment Grade
Maximum potential amount of future payments
Total amount outstanding	27,100,000,000	25,600,000,000
Non-Investment Grade | Financial standby letters of credit
Maximum potential amount of future payments
Total amount outstanding	11,800,000,000	10,900,000,000
Non-Investment Grade | Performance guarantees
Maximum potential amount of future payments
Total amount outstanding	2,100,000,000	2,400,000,000
Non-Investment Grade | Derivative instruments considered to be guarantees
Maximum potential amount of future payments
Total amount outstanding	0	0
Non-Investment Grade | Loans sold with recourse
Maximum potential amount of future payments
Total amount outstanding	0	0
Non-Investment Grade | Securities lending indemnifications
Maximum potential amount of future payments
Total amount outstanding	0	0
Non-Investment Grade | Credit card merchant processing
Maximum potential amount of future payments
Total amount outstanding	0	0
Non-Investment Grade | Credit card arrangements with partners
Maximum potential amount of future payments
Total amount outstanding	0	0
Non-Investment Grade | Custody indemnifications and other
Maximum potential amount of future payments
Total amount outstanding	13,200,000,000	12,300,000,000
Not Rated
Maximum potential amount of future payments
Total amount outstanding	324,100,000,000	303,700,000,000
Not Rated | Financial standby letters of credit
Maximum potential amount of future payments
Total amount outstanding	17,000,000,000	14,800,000,000
Not Rated | Performance guarantees
Maximum potential amount of future payments
Total amount outstanding	600,000,000	1,000,000,000
Not Rated | Derivative instruments considered to be guarantees
Maximum potential amount of future payments
Total amount outstanding	110,900,000,000	95,900,000,000
Not Rated | Loans sold with recourse
Maximum potential amount of future payments
Total amount outstanding	1,200,000,000	1,400,000,000
Not Rated | Securities lending indemnifications
Maximum potential amount of future payments
Total amount outstanding	98,300,000,000	103,700,000,000
Not Rated | Credit card merchant processing
Maximum potential amount of future payments
Total amount outstanding	95,000,000,000	85,500,000,000
Not Rated | Credit card arrangements with partners
Maximum potential amount of future payments
Total amount outstanding	1,100,000,000	1,400,000,000
Not Rated | Custody indemnifications and other
Maximum potential amount of future payments
Total amount outstanding	$ 0	$ 0