Investments (Distribution Of Securities By Percentage Of Fair Value Below Book Value By More Than 5% For A Continuous Twelve Month Period Or Longer) (Detail) - Unrealized loss position > 12 months $ in Millions	Sep. 30, 2019 USD ($) security
> 5% To 15% [Member]
Available For Sale Securities [Abstract]
Number of available-for-sale securities in unrealized loss position | security	9
Fixed-maturity securities held as available-for-sale, amortized cost	$ 19
Available For Sale Securities	$ 19
> 15% To 25% [Member]
Available For Sale Securities [Abstract]
Number of available-for-sale securities in unrealized loss position | security	1
Fixed-maturity securities held as available-for-sale, amortized cost	$ 1
Available For Sale Securities	$ 0
> 25% To 50% [Member]
Available For Sale Securities [Abstract]
Number of available-for-sale securities in unrealized loss position | security	2
Fixed-maturity securities held as available-for-sale, amortized cost	$ 14
Available For Sale Securities	$ 10
> 50% [Member]
Available For Sale Securities [Abstract]
Number of available-for-sale securities in unrealized loss position | security	3
Fixed-maturity securities held as available-for-sale, amortized cost	$ 63
Available For Sale Securities	$ 30
Greater Than 5% [Member]
Available For Sale Securities [Abstract]
Number of available-for-sale securities in unrealized loss position | security	15
Fixed-maturity securities held as available-for-sale, amortized cost	$ 97
Available For Sale Securities	$ 59