HELD-TO-MATURITY SECURITIES - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Held-to-maturity Securities [Abstract]
Available-for-sale securities transferred to held-to-maturity securities	$ 1,000,000,000	$ 2,870,000,000
Unrealized Net Losses Recognized In OCI At Time Of Transfer Of Available For Sale Securities Transferred To Held To Maturity Securities	14,000,000
Unrealized Net Gains Recognized In OCI At Time Of Transfer Of Available For Sale Securities Transferred To Held To Maturity Securities	58,000,000
Other than temporary impairment losses, held-to-maturity	$ 0	$ 0