Investments (Distribution By Contractual Maturity Of Available-For-Sale and Held-To-Maturity Investments) (Detail) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
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	901	$ 916
Fixed Maturities [Member]
Available For Sale Securities [Abstract]
Due in one year or less	790
Due after one year through five years	677
Due after five years through ten years	670
Due after ten years	1,047
Mortgage-Backed and Asset-Backed	668
Total Available-For-Sale, amortized cost	3,852
Due in one year or less	802
Due after one year through five years	702
Due after five years through ten years	589
Due after ten years	1,073
Mortgage-Backed and Asset-Backed	657
Total Available-For-Sale, fair value	3,823
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	901
Mortgage-Backed and Asset-Backed	0
Held-To-Maturity Securities Fair Value	$ 901