Annual report pursuant to Section 13 and 15(d)

AVAILABLE-FOR-SALE AND OTHER SECURITIES - Security Impairment (Details)

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AVAILABLE-FOR-SALE AND OTHER SECURITIES - Security Impairment (Details) - USD ($)
$ in Millions
9 Months Ended 12 Months Ended
Sep. 30, 2017
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]        
Impairment losses recognized in earnings on available-for-sale securities $ (4) $ (4) $ (2) $ (2)
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Roll Forward]        
Balance, beginning of year $ 12 12 18 31
Reductions from sales   (15) (8) (15)
Credit losses not previously recognized   4 2 0
Additional credit losses   0 0 2
Balance, end of year   1 12 18
Collateralized Debt Obligations        
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]        
Impairment losses recognized in earnings on available-for-sale securities   (4) 0 (2)
Municipal Securities        
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]        
Impairment losses recognized in earnings on available-for-sale securities   $ 0 $ (2) $ 0