INVESTMENTS - Recognition and Measurement of OTTI (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
OTTI on Investments disclosures
Total OTTI losses recognized during the period		$ 2	$ 4	$ 34
Less: portion of impairment loss recognized in AOCI (before taxes)	[1]	0	0	0
Net impairment losses recognized in earnings for securities that the Company does not intend to sell nor will likely be required to sell		2	4	34
Impairment losses recognized in earnings for securities that the Company intends to sell, would be more-likely-than-not required to sell or will be subject to an issuer call deemed probable of exercise		61	616	231
Total impairment losses recognized in earnings	[1]	63	620	265
Securities available-for-sale (AFS)
OTTI on Investments disclosures
Total OTTI losses recognized during the period		2	3	33
Less: portion of impairment loss recognized in AOCI (before taxes)		0	0	0
Net impairment losses recognized in earnings for securities that the Company does not intend to sell nor will likely be required to sell		2	3	33
Impairment losses recognized in earnings for securities that the Company intends to sell, would be more-likely-than-not required to sell or will be subject to an issuer call deemed probable of exercise		59	246	182
Total impairment losses recognized in earnings		61	249	215
Held-to-maturity Securities
OTTI on Investments disclosures
Total OTTI losses recognized during the period		0	1	1
Less: portion of impairment loss recognized in AOCI (before taxes)		0	0	0
Net impairment losses recognized in earnings for securities that the Company does not intend to sell nor will likely be required to sell		0	1	1
Impairment losses recognized in earnings for securities that the Company intends to sell, would be more-likely-than-not required to sell or will be subject to an issuer call deemed probable of exercise		2	38	43
Total impairment losses recognized in earnings		2	39	44
Other assets
OTTI on Investments disclosures
Total OTTI losses recognized during the period		0	0	0
Less: portion of impairment loss recognized in AOCI (before taxes)		0	0	0
Net impairment losses recognized in earnings for securities that the Company does not intend to sell nor will likely be required to sell		0	0	0
Impairment losses recognized in earnings for securities that the Company intends to sell, would be more-likely-than-not required to sell or will be subject to an issuer call deemed probable of exercise		0	332	6
Total impairment losses recognized in earnings		$ 0	332	$ 6
Venezuelan bolívar fuerte | Securities available-for-sale (AFS)
OTTI on Investments disclosures
Total impairment losses recognized in earnings			$ 160

[1] Certain prior-period revenue and expense lines and totals were reclassified to conform to the current period’s presentation. See Note 3 to the Consolidated Financial Statements.