Business Developments And Risks And Uncertainties (Assets And Liabilities Held For Sale) (Detail) $ in Millions	Dec. 31, 2016 USD ($)
Assets And Liabilities Held For Sale By Major Category [Line Items]
Assets held for sale	$ 555
Liabilities held for sale	346
Investments At Fair Value [Member]
Assets And Liabilities Held For Sale By Major Category [Line Items]
Assets held for sale	466
Cash And Cash Equivalents [Member]
Assets And Liabilities Held For Sale By Major Category [Line Items]
Assets held for sale	73
Premiums Receivable [Member]
Assets And Liabilities Held For Sale By Major Category [Line Items]
Assets held for sale	267
Other Assets [Member]
Assets And Liabilities Held For Sale By Major Category [Line Items]
Assets held for sale	19
Valuation Allowance [Member]
Assets And Liabilities Held For Sale By Major Category [Line Items]
Assets held for sale	(270)
Unearned Premium Revenue [Member]
Assets And Liabilities Held For Sale By Major Category [Line Items]
Liabilities held for sale	304
Other Liabilities [Member]
Assets And Liabilities Held For Sale By Major Category [Line Items]
Liabilities held for sale	$ 42