Investments (Distribution By Contractual Maturity Of Available-For-Sale and Held-To-Maturity Investments) (Detail) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Variable Interest Entity Primary Beneficiary [Member]
Held To Maturity Securities [Abstract]
Total held-to-maturity, amortized cost	$ 890	$ 890
Held-To-Maturity Securities Fair Value	897	$ 876
Fixed Maturities [Member]
Available For Sale Securities [Abstract]
Due in one year or less	508
Due after one year through five years	874
Due after five years through ten years	684
Due after ten years	1,270
Mortgage-Backed and Asset-Backed	1,167
Total Available-For-Sale, amortized cost	4,503
Due in one year or less	509
Due after one year through five years	883
Due after five years through ten years	635
Due after ten years	1,348
Mortgage-Backed and Asset-Backed	1,160
Total Available-For-Sale, fair value	4,535
Fixed Maturities [Member] | Variable Interest Entity Primary Beneficiary [Member]
Held To Maturity Securities [Abstract]
Due in one year or less	0
Due after one year through five years	0
Due after five years through ten years	0
Due after ten years	890
Mortgage-Backed and Asset-Backed	0
Total held-to-maturity, amortized cost	890
Due in one year or less	0
Due after one year through five years	0
Due after five years through ten years	0
Due after ten years	897
Mortgage-Backed and Asset-Backed	0
Held-To-Maturity Securities Fair Value	$ 897