INVESTMENTS - Debt Securities in HTM in Unrecognized Loss Position (Details) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value
Less than 12 months	$ 914	$ 3,532
12 months or longer	13,542	20,889
Total	14,456	24,421
Held-to-maturity Securities, Continuous Unrealized Loss Position, Gross Recognized Losses
Less than 12 months	22	84
12 months or longer	170	373
Total	192	457
Unrealized (loss), other than temporary impairment, not credit loss, recorded in AOCI	(67)	(496)
Mortgage-backed securities
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value
Less than 12 months	47	17
12 months or longer	10,147	17,176
Total	10,194	17,193
Held-to-maturity Securities, Continuous Unrealized Loss Position, Gross Recognized Losses
Less than 12 months	0	0
12 months or longer	78	188
Total	78	188
State and municipal securities
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value
Less than 12 months	242	2,200
12 months or longer	832	1,210
Total	1,074	3,410
Held-to-maturity Securities, Continuous Unrealized Loss Position, Gross Recognized Losses
Less than 12 months	6	58
12 months or longer	84	180
Total	90	238
Foreign government
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value
Less than 12 months	570	1,313
12 months or longer	0	0
Total	570	1,313
Held-to-maturity Securities, Continuous Unrealized Loss Position, Gross Recognized Losses
Less than 12 months	14	26
12 months or longer	0	0
Total	14	26
Asset-backed securities
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value
Less than 12 months	55	2
12 months or longer	2,563	2,503
Total	2,618	2,505
Held-to-maturity Securities, Continuous Unrealized Loss Position, Gross Recognized Losses
Less than 12 months	2	0
12 months or longer	8	5
Total	$ 10	$ 5