INVESTMENTS - Debt Securities Held-to-Maturity (Details) - USD ($) $ in Millions	1 Months Ended
	Dec. 31, 2019	Mar. 31, 2019	Nov. 30, 2018	Dec. 31, 2018
Debt Securities Held-to-maturity
Carrying value	$ 80,775			$ 63,357
Gross unrecognized gains	1,557			386
Gross unrecognized losses	109			853
Fair value	82,223			62,890
Mortgage-backed securities - U.S. government-sponsored agency guaranteed
Debt Securities Held-to-maturity
Carrying value	46,637			34,239
Gross unrecognized gains	1,047			199
Gross unrecognized losses	21			578
Fair value	47,663			33,860
Mortgage-backed securities - Non-U.S. residential
Debt Securities Held-to-maturity
Carrying value	1,039			1,339
Gross unrecognized gains	5			12
Gross unrecognized losses	0			1
Fair value	1,044			1,350
Mortgage-backed securities - Commercial
Debt Securities Held-to-maturity
Carrying value	582			368
Gross unrecognized gains	1			0
Gross unrecognized losses	0			0
Fair value	583			368
Mortgage-backed securities
Debt Securities Held-to-maturity
Carrying value	48,258			35,946
Gross unrecognized gains	1,053			211
Gross unrecognized losses	21			579
Fair value	49,290			35,578
Fair value of securities transferred from AFS to HTM		$ 5,000	$ 10,000
Unrealized loss position of securities at time of transfer		$ 56	$ 598
State and municipal securities
Debt Securities Held-to-maturity
Carrying value	9,104			7,628
Gross unrecognized gains	455			167
Gross unrecognized losses	28			138
Fair value	9,531			7,657
Fair value of securities transferred from AFS to HTM	173
Bonds in unrealized gain position	5
Foreign government
Debt Securities Held-to-maturity
Carrying value	1,934			1,027
Gross unrecognized gains	37			0
Gross unrecognized losses	1			24
Fair value	1,970			1,003
Asset-backed securities
Debt Securities Held-to-maturity
Carrying value	21,479			18,756
Gross unrecognized gains	12			8
Gross unrecognized losses	59			112
Fair value	$ 21,432			$ 18,652