INVESTMENTS - Debt Securities Held-to-Maturity (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Debt Securities Held-to-maturity
Amortized cost	$ 82,391	$ 80,775
Total allowance for credit losses on HTM	76	0
Carrying value, net	82,315	80,775
Gross unrealized gains	2,571	1,557
Gross unrealized losses	1,304	109
Fair value	83,582	82,223
Fair value, allowance for securities HTM at end of period	(76)
Fair value, net	83,582
Mortgage-backed securities - U.S. agency-sponsored
Debt Securities Held-to-maturity
Amortized cost	48,270	46,637
Gross unrealized gains	2,010	1,047
Gross unrealized losses	16	21
Fair value	50,264	47,663
Mortgage-backed securities - Non-U.S. residential
Debt Securities Held-to-maturity
Amortized cost	1,112	1,039
Gross unrealized gains	0	5
Gross unrealized losses	12	0
Fair value	1,100	1,044
Commercial and other
Debt Securities Held-to-maturity
Amortized cost	654	582
Gross unrealized gains	1	1
Gross unrealized losses	0	0
Fair value	655	583
Mortgage-backed securities
Debt Securities Held-to-maturity
Amortized cost	50,036	48,258
Gross unrealized gains	2,011	1,053
Gross unrealized losses	28	21
Fair value	52,019	49,290
State and municipal securities
Debt Securities Held-to-maturity
Amortized cost	9,269	9,104
Total allowance for credit losses on HTM	66	0
Gross unrealized gains	516	455
Gross unrealized losses	25	28
Fair value	9,760	9,531
Foreign government
Debt Securities Held-to-maturity
Amortized cost	1,553	1,934
Total allowance for credit losses on HTM	4	0
Gross unrealized gains	40	37
Gross unrealized losses	0	1
Fair value	1,593	1,970
Asset-backed securities
Debt Securities Held-to-maturity
Amortized cost	21,533	21,479
Total allowance for credit losses on HTM	6	0
Gross unrealized gains	4	12
Gross unrealized losses	1,251	59
Fair value	$ 20,286	$ 21,432