INVESTMENTS - Debt Securities in HTM in Unrecognized Loss Position (Details) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value
Less than 12 months	$ 1,290	$ 3,532
12 months or longer	15,078	20,889
Total	16,368	24,421
Held-to-maturity Securities, Continuous Unrealized Loss Position, Gross Recognized Losses
Less than 12 months	61	84
12 months or longer	206	373
Total	267	457
Unrealized (loss), other than temporary impairment, not credit loss, recorded in AOCI	(76)	(496)
Mortgage-backed securities
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value
Less than 12 months	35	17
12 months or longer	11,533	17,176
Total	11,568	17,193
Held-to-maturity Securities, Continuous Unrealized Loss Position, Gross Recognized Losses
Less than 12 months	1	0
12 months or longer	113	188
Total	114	188
State and municipal securities
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value
Less than 12 months	629	2,200
12 months or longer	735	1,210
Total	1,364	3,410
Held-to-maturity Securities, Continuous Unrealized Loss Position, Gross Recognized Losses
Less than 12 months	43	58
12 months or longer	89	180
Total	132	238
Foreign government
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value
Less than 12 months	572	1,313
12 months or longer	0	0
Total	572	1,313
Held-to-maturity Securities, Continuous Unrealized Loss Position, Gross Recognized Losses
Less than 12 months	16	26
12 months or longer	0	0
Total	16	26
Asset-backed securities
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value
Less than 12 months	54	2
12 months or longer	2,810	2,503
Total	2,864	2,505
Held-to-maturity Securities, Continuous Unrealized Loss Position, Gross Recognized Losses
Less than 12 months	1	0
12 months or longer	4	5
Total	$ 5	$ 5