INVESTMENTS - Fair Value of AFS Debt Securities by Contractual Maturity Date (Details) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016
Amortized cost
Total amortized cost	$ 293,374	$ 299,892
Fair value
Total fair value	293,196	299,033
Mortgage-backed securities
Amortized cost
Due within 1 year, amortized cost	96	132
After 1 but within 5 years, amortized cost	812	736
After 5 but within 10 years, amortized cost	1,733	2,279
After 10 years, amortized cost	44,222	39,770
Total amortized cost	46,863	42,917
Fair value
Fair value, due within 1 year	96	132
Fair value, after 1 but within 5 years	814	738
Fair value, after 5 but within 10 years	1,730	2,265
Fair value, after 10 years	44,079	39,538
Total fair value	46,719	42,673
U.S. Treasury and federal agency securities
Amortized cost
Due within 1 year, amortized cost	3,183	4,945
After 1 but within 5 years, amortized cost	103,151	101,369
After 5 but within 10 years, amortized cost	6,211	17,153
After 10 years, amortized cost	35	91
Total amortized cost	112,580	123,558
Fair value
Fair value, due within 1 year	3,165	4,945
Fair value, after 1 but within 5 years	103,156	101,323
Fair value, after 5 but within 10 years	6,240	17,314
Fair value, after 10 years	37	89
Total fair value	112,598	123,671
State and municipal securities
Amortized cost
Due within 1 year, amortized cost	2,217	2,093
After 1 but within 5 years, amortized cost	2,393	2,668
After 5 but within 10 years, amortized cost	464	335
After 10 years, amortized cost	4,626	5,701
Total amortized cost	9,700	10,797
Fair value
Fair value, due within 1 year	2,217	2,092
Fair value, after 1 but within 5 years	2,396	2,662
Fair value, after 5 but within 10 years	478	334
Fair value, after 10 years	4,448	5,032
Total fair value	9,539	10,120
Foreign government
Amortized cost
Due within 1 year, amortized cost	31,792	32,540
After 1 but within 5 years, amortized cost	54,028	51,008
After 5 but within 10 years, amortized cost	13,457	12,388
After 10 years, amortized cost	2,392	2,176
Total amortized cost	101,669	98,112
Fair value
Fair value, due within 1 year	31,800	32,547
Fair value, after 1 but within 5 years	53,507	50,881
Fair value, after 5 but within 10 years	13,944	12,440
Fair value, after 10 years	2,531	2,280
Total fair value	101,782	98,148
All other
Amortized cost
Due within 1 year, amortized cost	3,794	2,629
After 1 but within 5 years, amortized cost	10,380	12,339
After 5 but within 10 years, amortized cost	5,760	6,566
After 10 years, amortized cost	2,628	2,974
Total amortized cost	22,562	24,508
Fair value
Fair value, due within 1 year	3,688	2,628
Fair value, after 1 but within 5 years	10,396	12,334
Fair value, after 5 but within 10 years	5,865	6,528
Fair value, after 10 years	2,609	2,931
Total fair value	$ 22,558	$ 24,421