INVESTMENTS - Fair Value of AFS Debt Securities by Contractual Maturity Date (Details) - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014
Available-for-sale Securities, Debt Maturities
Total amortized cost	$ 293,107	$ 296,920
Total fair value	293,155	297,418
Mortgage-backed securities
Available-for-sale Securities, Debt Maturities
Due within 1 year, amortized cost	40	44
After 1 but within 5 years, amortized cost	940	931
After 5 but within 10 years, amortized cost	1,162	1,362
After 10 years, amortized cost	39,539	42,163
Total amortized cost	41,681	44,500
Fair value, due within 1 year	40	44
Fair value, after 1 but within 5 years	946	935
Fair value, after 5 but within 10 years	1,177	1,387
Fair value, after 10 years	39,832	42,642
Total fair value	41,995	45,008
U.S. Treasury and federal agency securities
Available-for-sale Securities, Debt Maturities
Due within 1 year, amortized cost	3,762	13,070
After 1 but within 5 years, amortized cost	114,168	104,982
After 5 but within 10 years, amortized cost	4,866	2,286
After 10 years, amortized cost	1,456	3,079
Total amortized cost	124,252	123,417
Fair value, due within 1 year	3,763	13,084
Fair value, after 1 but within 5 years	114,654	105,131
Fair value, after 5 but within 10 years	4,831	2,325
Fair value, after 10 years	1,422	3,150
Total fair value	124,670	123,690
State and municipal securities
Available-for-sale Securities, Debt Maturities
Due within 1 year, amortized cost	1,047	652
After 1 but within 5 years, amortized cost	3,965	4,387
After 5 but within 10 years, amortized cost	513	524
After 10 years, amortized cost	7,012	7,963
Total amortized cost	12,537	13,526
Fair value, due within 1 year	1,045	651
Fair value, after 1 but within 5 years	3,966	4,381
Fair value, after 5 but within 10 years	523	537
Fair value, after 10 years	6,179	7,130
Total fair value	11,713	12,699
Foreign government
Available-for-sale Securities, Debt Maturities
Due within 1 year, amortized cost	31,715	31,355
After 1 but within 5 years, amortized cost	39,770	41,913
After 5 but within 10 years, amortized cost	15,341	16,008
After 10 years, amortized cost	679	973
Total amortized cost	87,505	90,249
Fair value, due within 1 year	31,737	31,382
Fair value, after 1 but within 5 years	39,771	42,467
Fair value, after 5 but within 10 years	15,376	15,779
Fair value, after 10 years	712	1,069
Total fair value	87,596	90,697
All other
Available-for-sale Securities, Debt Maturities
Due within 1 year, amortized cost	1,458	1,248
After 1 but within 5 years, amortized cost	12,873	10,442
After 5 but within 10 years, amortized cost	7,947	7,282
After 10 years, amortized cost	4,854	6,256
Total amortized cost	27,132	25,228
Fair value, due within 1 year	1,460	1,251
Fair value, after 1 but within 5 years	12,941	10,535
Fair value, after 5 but within 10 years	7,948	7,318
Fair value, after 10 years	4,832	6,220
Total fair value	$ 27,181	$ 25,324