INVESTMENTS - Fair Value of AFS Debt Securities by Contractual Maturity Date (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Available-for-sale Securities, Debt Maturities
Total amortized cost	$ 292,622	$ 296,920
Total fair value	294,249	297,418
Mortgage-backed securities
Available-for-sale Securities, Debt Maturities
Due within 1 year, amortized cost	31	44
After 1 but within 5 years, amortized cost	904	931
After 5 but within 10 years, amortized cost	1,292	1,362
After 10 years, amortized cost	43,924	42,163
Total amortized cost	46,151	44,500
Fair value, due within 1 year	31	44
Fair value, after 1 but within 5 years	914	935
Fair value, after 5 but within 10 years	1,311	1,387
Fair value, after 10 years	44,611	42,642
Total fair value	46,867	45,008
U.S. Treasury and federal agency securities
Available-for-sale Securities, Debt Maturities
Due within 1 year, amortized cost	7,218	13,070
After 1 but within 5 years, amortized cost	104,763	104,982
After 5 but within 10 years, amortized cost	4,812	2,286
After 10 years, amortized cost	3,461	3,079
Total amortized cost	120,254	123,417
Fair value, due within 1 year	7,243	13,084
Fair value, after 1 but within 5 years	105,781	105,131
Fair value, after 5 but within 10 years	4,855	2,325
Fair value, after 10 years	3,480	3,150
Total fair value	121,359	123,690
State and municipal securities
Available-for-sale Securities, Debt Maturities
Due within 1 year, amortized cost	1,389	652
After 1 but within 5 years, amortized cost	3,896	4,387
After 5 but within 10 years, amortized cost	549	524
After 10 years, amortized cost	7,191	7,963
Total amortized cost	13,025	13,526
Fair value, due within 1 year	1,327	651
Fair value, after 1 but within 5 years	3,840	4,381
Fair value, after 5 but within 10 years	567	537
Fair value, after 10 years	6,511	7,130
Total fair value	12,245	12,699
Foreign government
Available-for-sale Securities, Debt Maturities
Due within 1 year, amortized cost	32,155	31,355
After 1 but within 5 years, amortized cost	38,055	41,913
After 5 but within 10 years, amortized cost	15,493	16,008
After 10 years, amortized cost	951	973
Total amortized cost	86,654	90,249
Fair value, due within 1 year	32,056	31,382
Fair value, after 1 but within 5 years	38,184	42,467
Fair value, after 5 but within 10 years	15,808	15,779
Fair value, after 10 years	1,011	1,069
Total fair value	87,059	90,697
All other
Available-for-sale Securities, Debt Maturities
Due within 1 year, amortized cost	1,662	1,248
After 1 but within 5 years, amortized cost	12,024	10,442
After 5 but within 10 years, amortized cost	7,957	7,282
After 10 years, amortized cost	4,895	6,256
Total amortized cost	26,538	25,228
Fair value, due within 1 year	1,665	1,251
Fair value, after 1 but within 5 years	12,137	10,535
Fair value, after 5 but within 10 years	8,026	7,318
Fair value, after 10 years	4,891	6,220
Total fair value	$ 26,719	$ 25,324