INVESTMENTS - Debt Securities Held-to-Maturity (Details) - USD ($) $ in Millions	1 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Debt Securities Held-to-maturity
Carrying value	$ 66,842	$ 63,357
Gross unrealized gains	697	386
Gross unrealized losses	465	853
Fair value	67,074	62,890
Mortgage-backed securities - U.S. agency-sponsored
Debt Securities Held-to-maturity
Carrying value	38,286	34,239
Gross unrealized gains	392	199
Gross unrealized losses	296	578
Fair value	38,382	33,860
Mortgage-backed securities - Non-U.S. residential
Debt Securities Held-to-maturity
Carrying value	1,313	1,339
Gross unrealized gains	13	12
Gross unrealized losses	1	1
Fair value	1,325	1,350
Commercial and other
Debt Securities Held-to-maturity
Carrying value	424	368
Gross unrealized gains	1	0
Gross unrealized losses	1	0
Fair value	424	368
Mortgage-backed securities
Debt Securities Held-to-maturity
Carrying value	40,023	35,946
Gross unrealized gains	406	211
Gross unrealized losses	298	579
Fair value	40,131	35,578
Transfer from AFS classification to HTM classification	5,000
Securities in unrealized loss position	56
State and municipal securities
Debt Securities Held-to-maturity
Carrying value	7,648	7,628
Gross unrealized gains	285	167
Gross unrealized losses	70	138
Fair value	7,863	7,657
Foreign government
Debt Securities Held-to-maturity
Carrying value	1,000	1,027
Gross unrealized gains	0	0
Gross unrealized losses	11	24
Fair value	989	1,003
Asset-backed securities
Debt Securities Held-to-maturity
Carrying value	18,171	18,756
Gross unrealized gains	6	8
Gross unrealized losses	86	112
Fair value	$ 18,091	$ 18,652