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) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Available For Sale Securities [Abstract]
Fixed-maturity securities held as available-for-sale, amortized cost	$ 6,444	$ 6,509
Available For Sale Securities	6,539	6,571
Held To Maturity Securities [Abstract]
Held-To-Maturity Securities Amortized Cost	2,742	2,757
Held-To-Maturity Securities Fair Value	2,635	2,632
> 5% To 15% [Member]
Held To Maturity Securities [Abstract]
Percentage Of Fair Value Below Book Value Minimum	5.00%
Percentage Of Fair Value Below Book Value Maximum	15.00%
> 5% To 15% [Member] | Unrealized loss position > 12 months
Available For Sale Securities [Abstract]
Number of available-for-sale securities in unrealized loss position	6
Fixed-maturity securities held as available-for-sale, amortized cost	49
Available For Sale Securities	44
Held To Maturity Securities [Abstract]
Number of Held-To-Maturity Securities in unrealized loss position	0
Held-To-Maturity Securities Amortized Cost	0
Held-To-Maturity Securities Fair Value	0
> 15% To 25% [Member]
Held To Maturity Securities [Abstract]
Percentage Of Fair Value Below Book Value Minimum	15.00%
Percentage Of Fair Value Below Book Value Maximum	25.00%
> 15% To 25% [Member] | Unrealized loss position > 12 months
Available For Sale Securities [Abstract]
Number of available-for-sale securities in unrealized loss position	3
Fixed-maturity securities held as available-for-sale, amortized cost	19
Available For Sale Securities	15
Held To Maturity Securities [Abstract]
Number of Held-To-Maturity Securities in unrealized loss position	0
Held-To-Maturity Securities Amortized Cost	0
Held-To-Maturity Securities Fair Value	0
> 25% To 50% [Member]
Held To Maturity Securities [Abstract]
Percentage Of Fair Value Below Book Value Minimum	25.00%
Percentage Of Fair Value Below Book Value Maximum	50.00%
> 25% To 50% [Member] | Unrealized loss position > 12 months
Available For Sale Securities [Abstract]
Number of available-for-sale securities in unrealized loss position	2
Fixed-maturity securities held as available-for-sale, amortized cost	41
Available For Sale Securities	29
Held To Maturity Securities [Abstract]
Number of Held-To-Maturity Securities in unrealized loss position	1
Held-To-Maturity Securities Amortized Cost	575
Held-To-Maturity Securities Fair Value	393
> 50% [Member]
Held To Maturity Securities [Abstract]
Percentage Of Fair Value Below Book Value Minimum	50.00%
> 50% [Member] | Unrealized loss position > 12 months
Available For Sale Securities [Abstract]
Number of available-for-sale securities in unrealized loss position	3
Fixed-maturity securities held as available-for-sale, amortized cost	130
Available For Sale Securities	12
Held To Maturity Securities [Abstract]
Number of Held-To-Maturity Securities in unrealized loss position	0
Held-To-Maturity Securities Amortized Cost	0
Held-To-Maturity Securities Fair Value	0
Greater Than 5% [Member] | Unrealized loss position > 12 months
Available For Sale Securities [Abstract]
Number of available-for-sale securities in unrealized loss position	14
Fixed-maturity securities held as available-for-sale, amortized cost	239
Available For Sale Securities	100
Held To Maturity Securities [Abstract]
Number of Held-To-Maturity Securities in unrealized loss position	1
Held-To-Maturity Securities Amortized Cost	575
Held-To-Maturity Securities Fair Value	$ 393