Investments - Additional Information (Detail) - USD ($)	Mar. 31, 2017	Dec. 31, 2016
Investments, Debt and Equity Securities [Abstract]
Net unrealized gains on investments included in "AOCI"	$ 949,000,000	$ 909,000,000
Additional other than temporary impairment losses	$ 0

Additional Other Than Temporary Impairment Losses Investments Available For Sale Securities

No definition available.

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration