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Investments (Credit Losses Recognized In Earnings Related To OTTI Losses Recognized In Accumulated Other Comprehensive Income (Loss)) (Detail) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Other than temporary impairment credit lossesfor available for sale securities rollforward [Abstract]      
Beginning Balance $ 29 $ 26 $ 16
Additions For Credit Loss Impairments Recognized In The Current Period On Securities Not Previous Impaired 11 0 0
Additions For Credit Loss Impairments Recognized In The Current Period On Securities Previously Impaired 5 4 10
Reductions For Credit Loss Impairments Previously Recognized On Securities Sold During The Period (2) (1) 0
Reductions For Credit Loss Impairments Previously Recognized On Securities Impaired To Fair Value During The Period (11) 0 0
Ending Balance $ 32 $ 29 $ 26