INVESTMENTS - Fair Value of AFS Debt Securities by Contractual Maturity Date (Details) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015
Available-for-sale Securities, Debt Maturities, Single Maturity Date, Amortized Cost Basis [Abstract]
Total amortized cost	$ 303,923	$ 299,600
Available-for-sale Securities, Debt Maturities, Single Maturity Date [Abstract]
Total fair value	306,792	298,511
Mortgage-backed securities
Available-for-sale Securities, Debt Maturities, Single Maturity Date, Amortized Cost Basis [Abstract]
Due within 1 year, amortized cost	176	114
After 1 but within 5 years, amortized cost	843	1,408
After 5 but within 10 years, amortized cost	2,246	1,750
After 10 years, amortized cost	44,038	42,846
Total amortized cost	47,303	46,118
Available-for-sale Securities, Debt Maturities, Single Maturity Date [Abstract]
Fair value, due within 1 year	176	114
Fair value, after 1 but within 5 years	850	1,411
Fair value, after 5 but within 10 years	2,300	1,751
Fair value, after 10 years	44,731	42,995
Total fair value	48,057	46,271
U.S. Treasury and federal agency
Available-for-sale Securities, Debt Maturities, Single Maturity Date, Amortized Cost Basis [Abstract]
Due within 1 year, amortized cost	3,020	3,016
After 1 but within 5 years, amortized cost	104,323	107,034
After 5 but within 10 years, amortized cost	12,217	12,786
After 10 years, amortized cost	98	355
Total amortized cost	119,658	123,191
Available-for-sale Securities, Debt Maturities, Single Maturity Date [Abstract]
Fair value, due within 1 year	3,022	3,014
Fair value, after 1 but within 5 years	105,934	106,878
Fair value, after 5 but within 10 years	12,655	12,684
Fair value, after 10 years	95	339
Total fair value	121,706	122,915
State and municipal securities
Available-for-sale Securities, Debt Maturities, Single Maturity Date, Amortized Cost Basis [Abstract]
Due within 1 year, amortized cost	2,157	3,289
After 1 but within 5 years, amortized cost	2,685	1,781
After 5 but within 10 years, amortized cost	459	502
After 10 years, amortized cost	6,402	6,527
Total amortized cost	11,703	12,099
Available-for-sale Securities, Debt Maturities, Single Maturity Date [Abstract]
Fair value, due within 1 year	2,155	3,287
Fair value, after 1 but within 5 years	2,693	1,781
Fair value, after 5 but within 10 years	469	516
Fair value, after 10 years	5,874	5,875
Total fair value	11,191	11,459
Foreign government
Available-for-sale Securities, Debt Maturities, Single Maturity Date, Amortized Cost Basis [Abstract]
Due within 1 year, amortized cost	28,878	25,898
After 1 but within 5 years, amortized cost	53,253	43,514
After 5 but within 10 years, amortized cost	12,952	17,013
After 10 years, amortized cost	2,550	2,326
Total amortized cost	97,633	88,751
Available-for-sale Securities, Debt Maturities, Single Maturity Date [Abstract]
Fair value, due within 1 year	28,898	25,905
Fair value, after 1 but within 5 years	53,089	43,464
Fair value, after 5 but within 10 years	13,479	16,968
Fair value, after 10 years	2,674	2,337
Total fair value	98,140	88,674
All other
Available-for-sale Securities, Debt Maturities, Single Maturity Date, Amortized Cost Basis [Abstract]
Due within 1 year, amortized cost	3,065	2,354
After 1 but within 5 years, amortized cost	13,637	14,035
After 5 but within 10 years, amortized cost	7,833	9,789
After 10 years, amortized cost	3,091	3,263
Total amortized cost	27,626	29,441
Available-for-sale Securities, Debt Maturities, Single Maturity Date [Abstract]
Fair value, due within 1 year	3,068	2,355
Fair value, after 1 but within 5 years	13,758	14,054
Fair value, after 5 but within 10 years	7,818	9,593
Fair value, after 10 years	3,054	3,190
Total fair value	$ 27,698	$ 29,192