INVESTMENTS - Fair Value of AFS Debt Securities by Contractual Maturity Date (Details) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Amortized cost
Total amortized cost	$ 295,297	$ 299,892
Fair value
Total fair value	295,011	299,033
Mortgage-backed securities
Amortized cost
Due within 1 year, amortized cost	61	132
After 1 but within 5 years, amortized cost	1,340	736
After 5 but within 10 years, amortized cost	1,469	2,279
After 10 years, amortized cost	42,882	39,770
Total amortized cost	45,752	42,917
Fair value
Fair value, due within 1 year	61	132
Fair value, after 1 but within 5 years	1,340	738
Fair value, after 5 but within 10 years	1,466	2,265
Fair value, after 10 years	42,783	39,538
Total fair value	45,650	42,673
U.S. Treasury and federal agency securities
Amortized cost
Due within 1 year, amortized cost	3,549	4,945
After 1 but within 5 years, amortized cost	109,477	101,369
After 5 but within 10 years, amortized cost	5,473	17,153
After 10 years, amortized cost	0	91
Total amortized cost	118,499	123,558
Fair value
Fair value, due within 1 year	3,539	4,945
Fair value, after 1 but within 5 years	109,286	101,323
Fair value, after 5 but within 10 years	5,501	17,314
Fair value, after 10 years	0	89
Total fair value	118,326	123,671
State and municipal securities
Amortized cost
Due within 1 year, amortized cost	2,036	2,093
After 1 but within 5 years, amortized cost	2,412	2,668
After 5 but within 10 years, amortized cost	493	335
After 10 years, amortized cost	4,394	5,701
Total amortized cost	9,335	10,797
Fair value
Fair value, due within 1 year	2,036	2,092
Fair value, after 1 but within 5 years	2,416	2,662
Fair value, after 5 but within 10 years	508	334
Fair value, after 10 years	4,230	5,032
Total fair value	9,190	10,120
Foreign government
Amortized cost
Due within 1 year, amortized cost	32,095	32,540
After 1 but within 5 years, amortized cost	52,519	51,008
After 5 but within 10 years, amortized cost	13,531	12,388
After 10 years, amortized cost	2,480	2,176
Total amortized cost	100,625	98,112
Fair value
Fair value, due within 1 year	32,097	32,547
Fair value, after 1 but within 5 years	52,362	50,881
Fair value, after 5 but within 10 years	13,690	12,440
Fair value, after 10 years	2,598	2,280
Total fair value	100,747	98,148
All other
Amortized cost
Due within 1 year, amortized cost	3,585	2,629
After 1 but within 5 years, amortized cost	9,799	12,339
After 5 but within 10 years, amortized cost	5,581	6,566
After 10 years, amortized cost	2,121	2,974
Total amortized cost	21,086	24,508
Fair value
Fair value, due within 1 year	3,583	2,628
Fair value, after 1 but within 5 years	9,818	12,334
Fair value, after 5 but within 10 years	5,585	6,528
Fair value, after 10 years	2,112	2,931
Total fair value	$ 21,098	$ 24,421