INVESTMENTS - Fair Value of AFS Debt Securities by Contractual Maturity Date (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Amoritzed cost
Investments	$ 433,253	$ 368,563
Fair value
Total fair value	342,256	280,265
Mortgage-backed securities
Amoritzed cost
Amortized cost, due within 1 year	290	20
Amortized cost, after 1 but within 5 years	609	573
Amortized cost, after 5 but within 10 years	1,010	594
Amortized cost, after 10 years	43,045	34,640
Amortized cost	44,954	35,827
Fair value
Fair value, due within 1 year	290	20
Fair value, after 1 but within 5 years	613	574
Fair value, after 5 but within 10 years	1,086	626
Fair value, after 10 years	44,123	34,877
Total fair value	46,112	36,097
U.S. Treasury and federal agency securities
Amoritzed cost
Amortized cost, due within 1 year	45,246	40,757
Amortized cost, after 1 but within 5 years	103,836	70,128
Amortized cost, after 5 but within 10 years	1,899	854
Amortized cost, after 10 years	272	26
Amortized cost	151,253	111,765
Fair value
Fair value, due within 1 year	45,397	40,688
Fair value, after 1 but within 5 years	106,417	69,850
Fair value, after 5 but within 10 years	1,964	851
Fair value, after 10 years	279	29
Total fair value	154,057	111,418
State and municipal
Amoritzed cost
Amortized cost, due within 1 year	391	932
Amortized cost, after 1 but within 5 years	559	714
Amortized cost, after 5 but within 10 years	303	195
Amortized cost, after 10 years	3,886	3,183
Amortized cost	5,139	5,024
Fair value
Fair value, due within 1 year	392	932
Fair value, after 1 but within 5 years	570	723
Fair value, after 5 but within 10 years	329	215
Fair value, after 10 years	3,730	3,108
Total fair value	5,021	4,978
Foreign government
Amoritzed cost
Amortized cost, due within 1 year	46,614	42,611
Amortized cost, after 1 but within 5 years	65,217	58,820
Amortized cost, after 5 but within 10 years	5,567	8,192
Amortized cost, after 10 years	2,007	1,335
Amortized cost	119,405	110,958
Fair value
Fair value, due within 1 year	46,815	42,666
Fair value, after 1 but within 5 years	66,383	59,071
Fair value, after 5 but within 10 years	5,702	8,198
Fair value, after 10 years	2,040	1,368
Total fair value	120,940	111,303
All other
Amoritzed cost
Amortized cost, due within 1 year	6,161	7,306
Amortized cost, after 1 but within 5 years	8,769	8,279
Amortized cost, after 5 but within 10 years	1,005	818
Amortized cost, after 10 years	144	116
Amortized cost	16,079	16,519
Fair value
Fair value, due within 1 year	6,187	7,311
Fair value, after 1 but within 5 years	8,841	8,275
Fair value, after 5 but within 10 years	995	797
Fair value, after 10 years	103	86
Total fair value	$ 16,126	$ 16,469