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	Dec. 31, 2022 USD ($) security
> 5% To 15% [Member]
Available For Sale Securities [Abstract]
Number of securities | security	72
Book Value	$ 129
Fair Value	$ 117
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%
> 15% To 25% [Member]
Available For Sale Securities [Abstract]
Number of securities | security	63
Book Value	$ 117
Fair Value	$ 93
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%
> 25% To 50% [Member]
Available For Sale Securities [Abstract]
Number of securities | security	53
Book Value	$ 84
Fair Value	$ 56
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%
> 50% [Member]
Available For Sale Securities [Abstract]
Number of securities | security	2
Book Value	$ 0
Fair Value	$ 0
Held To Maturity Securities [Abstract]
Percentage Of Fair Value Below Book Value Minimum	50.00%
Greater Than 5% [Member]
Available For Sale Securities [Abstract]
Number of securities | security	190
Book Value	$ 330
Fair Value	$ 266