INVESTMENTS - Cumulative OTTI Credit Losses (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2018
Schedule of other than temporary impairment, credit losses recognized in earnings, disclosures
Held-to-maturity debt securities (including $971 and $435 pledged to creditors as of December 31, 2018 and 2017, respectively)	$ 63,357	$ 53,320
Schedule of other-than-temporary impairment, credit losses recognized in earnings, roll forward
Available-for-sale debt securities (including $9,289 and $9,493 pledged to creditors as of December 31, 2018 and 2017, respectively)	288,038	290,725
Mortgage-backed securities
Schedule of other than temporary impairment, credit losses recognized in earnings, disclosures
Held-to-maturity debt securities (including $971 and $435 pledged to creditors as of December 31, 2018 and 2017, respectively)	35,946	26,099
Schedule of other-than-temporary impairment, credit losses recognized in earnings, roll forward
Cumulative OTTI reclassified from HTM to AFS	18	38
Available-for-sale debt securities (including $9,289 and $9,493 pledged to creditors as of December 31, 2018 and 2017, respectively)	44,505	44,957
State and municipal securities
Schedule of other than temporary impairment, credit losses recognized in earnings, disclosures
Held-to-maturity debt securities (including $971 and $435 pledged to creditors as of December 31, 2018 and 2017, respectively)	7,628	8,897
Schedule of other-than-temporary impairment, credit losses recognized in earnings, roll forward
Available-for-sale debt securities (including $9,289 and $9,493 pledged to creditors as of December 31, 2018 and 2017, respectively)	9,206	8,765
Foreign government securities
Schedule of other than temporary impairment, credit losses recognized in earnings, disclosures
Held-to-maturity debt securities (including $971 and $435 pledged to creditors as of December 31, 2018 and 2017, respectively)	1,027	740
Schedule of other-than-temporary impairment, credit losses recognized in earnings, roll forward
Available-for-sale debt securities (including $9,289 and $9,493 pledged to creditors as of December 31, 2018 and 2017, respectively)	100,691	100,533
Corporate
Schedule of other-than-temporary impairment, credit losses recognized in earnings, roll forward
Available-for-sale debt securities (including $9,289 and $9,493 pledged to creditors as of December 31, 2018 and 2017, respectively)	11,599
Other debt securities
Schedule of other-than-temporary impairment, credit losses recognized in earnings, roll forward
Available-for-sale debt securities (including $9,289 and $9,493 pledged to creditors as of December 31, 2018 and 2017, respectively)	3,972
AFS debt securities
Schedule of other-than-temporary impairment, credit losses recognized in earnings, roll forward
Balance at beginning of period	48	31
Credit impairments recognized in earnings on securities not previously impaired	0	0
Credit impairments recognized in earnings on securities that have been previously impaired	0	2
Reductions due to credit-impaired securities sold, transferred or matured	(43)	15
Balance at end of period	5	48
AFS debt securities | Mortgage-backed securities
Schedule of other-than-temporary impairment, credit losses recognized in earnings, roll forward
Balance at beginning of period	38	0
Credit impairments recognized in earnings on securities not previously impaired	0	0
Credit impairments recognized in earnings on securities that have been previously impaired	0	0
Reductions due to credit-impaired securities sold, transferred or matured	(37)	38
Balance at end of period	1	38
AFS debt securities | State and municipal securities
Schedule of other-than-temporary impairment, credit losses recognized in earnings, roll forward
Balance at beginning of period	4	4
Credit impairments recognized in earnings on securities not previously impaired	0	0
Credit impairments recognized in earnings on securities that have been previously impaired	0	0
Reductions due to credit-impaired securities sold, transferred or matured	(4)	0
Balance at end of period	0	4
AFS debt securities | Foreign government securities
Schedule of other-than-temporary impairment, credit losses recognized in earnings, roll forward
Balance at beginning of period	0	0
Credit impairments recognized in earnings on securities not previously impaired	0	0
Credit impairments recognized in earnings on securities that have been previously impaired	0	0
Reductions due to credit-impaired securities sold, transferred or matured	0	0
Balance at end of period	0	0
AFS debt securities | Corporate
Schedule of other-than-temporary impairment, credit losses recognized in earnings, roll forward
Balance at beginning of period	4	5
Credit impairments recognized in earnings on securities not previously impaired	0	0
Credit impairments recognized in earnings on securities that have been previously impaired	0	0
Reductions due to credit-impaired securities sold, transferred or matured	0	(1)
Balance at end of period	4	4
AFS debt securities | Other debt securities
Schedule of other-than-temporary impairment, credit losses recognized in earnings, roll forward
Balance at beginning of period	2	22
Credit impairments recognized in earnings on securities not previously impaired	0	0
Credit impairments recognized in earnings on securities that have been previously impaired	0	2
Reductions due to credit-impaired securities sold, transferred or matured	(2)	(22)
Balance at end of period	0	2
HTM debt securities
Schedule of other-than-temporary impairment, credit losses recognized in earnings, roll forward
Balance at beginning of period	57	104
Credit impairments recognized in earnings on securities not previously impaired	0	0
Credit impairments recognized in earnings on securities that have been previously impaired	0	0
Reductions due to credit-impaired securities sold, transferred or matured	(57)	(47)
Balance at end of period	0	57
HTM debt securities | Mortgage-backed securities
Schedule of other-than-temporary impairment, credit losses recognized in earnings, roll forward
Balance at beginning of period	54	101
Credit impairments recognized in earnings on securities not previously impaired	0	0
Credit impairments recognized in earnings on securities that have been previously impaired	0	0
Reductions due to credit-impaired securities sold, transferred or matured	(54)	(47)
Balance at end of period	0	54
HTM debt securities | State and municipal securities
Schedule of other-than-temporary impairment, credit losses recognized in earnings, roll forward
Balance at beginning of period	3
Credit impairments recognized in earnings on securities not previously impaired	0
Credit impairments recognized in earnings on securities that have been previously impaired	0
Reductions due to credit-impaired securities sold, transferred or matured	(3)
Balance at end of period	0	3
HTM debt securities | Corporate
Schedule of other-than-temporary impairment, credit losses recognized in earnings, roll forward
Balance at beginning of period	$ 3	3
Credit impairments recognized in earnings on securities not previously impaired		0
Credit impairments recognized in earnings on securities that have been previously impaired		0
Reductions due to credit-impaired securities sold, transferred or matured		0
Balance at end of period		$ 3
ASU 2017-12
Schedule of other than temporary impairment, credit losses recognized in earnings, disclosures
Held-to-maturity debt securities (including $971 and $435 pledged to creditors as of December 31, 2018 and 2017, respectively)			$ (4,000)
Schedule of other-than-temporary impairment, credit losses recognized in earnings, roll forward
Available-for-sale debt securities (including $9,289 and $9,493 pledged to creditors as of December 31, 2018 and 2017, respectively)			$ 4,000