INVESTMENTS - Debt Securities in HTM in Unrecognized Loss Position (Details) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value
Less than 12 months	$ 3,189	$ 3,532
12 months or longer	21,331	20,889
Total	24,520	24,421
Held-to-maturity Securities, Continuous Unrealized Loss Position, Gross Recognized Losses
Less than 12 months	73	84
12 months or longer	382	373
Total	455	457
Unrealized (loss), other than temporary impairment, not credit loss, recorded in AOCI	(517)	(496)
Mortgage-backed securities
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value
Less than 12 months	3	17
12 months or longer	18,784	17,176
Total	18,787	17,193
Held-to-maturity Securities, Continuous Unrealized Loss Position, Gross Recognized Losses
Less than 12 months	0	0
12 months or longer	204	188
Total	204	188
State and municipal securities
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value
Less than 12 months	2,005	2,200
12 months or longer	1,199	1,210
Total	3,204	3,410
Held-to-maturity Securities, Continuous Unrealized Loss Position, Gross Recognized Losses
Less than 12 months	52	58
12 months or longer	172	180
Total	224	238
Foreign government
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value
Less than 12 months	1,181	1,313
12 months or longer	0	0
Total	1,181	1,313
Held-to-maturity Securities, Continuous Unrealized Loss Position, Gross Recognized Losses
Less than 12 months	21	26
12 months or longer	0	0
Total	21	26
Asset-backed securities
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value
Less than 12 months	0	2
12 months or longer	1,348	2,503
Total	1,348	2,505
Held-to-maturity Securities, Continuous Unrealized Loss Position, Gross Recognized Losses
Less than 12 months	0	0
12 months or longer	6	5
Total	$ 6	$ 5