Investments (Schedule Of Fixed Maturities By Contractual Maturity) (Detail) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Investments, Debt and Equity Securities [Abstract]
Available for sale, Due in 1 year or less, Amortized Cost	$ 3,736	$ 3,164
Available for sale, Due after 1 year through 5 years, Amortized Cost	26,694	24,749
Available for sale, Due after 5 years though 10 years, Amortized Cost	23,638	25,388
Available for sale, Due after 10 years, Amortized Cost	8,174	9,255
Available for sale, Mortgage-backed securities, Amortized Cost	16,395	15,279
Available for sale, at amortized cost	78,637	77,835
Available for sale, Due in 1 year or less, Fair Value	3,742	3,182
Available for sale, Due after 1 year through 5 years, Fair Value	26,646	25,068
Available for sale, Due after 5 years through 10 years, Fair Value	23,325	25,704
Available for sale, Due after 10 years, Fair Value	8,242	9,695
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Amortized Cost	62,242	62,556
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Fair Value	61,955	63,649
Available for sale, Mortgage backed securities, Fair Value	15,898	15,290
Available for sale, Fair Value	77,853	78,939
Held to maturity, Due in 1 year or less, Amortized Cost	567	743
Held to maturity, Due after 1 year through 5 years, Amortized Cost	2,959	2,669
Held to maturity, Due after 5 years through 10 years, Amortized Cost	4,507	4,744
Held to maturity, Due after 10 years, Amortized Cost	2,956	3,455
Held to maturity, Mortgage backed securities, Amortized Cost	2,574	2,724
Held to maturity, Amortized Cost	13,563	14,335
Held to maturity, Due in 1 year or less, Fair Value	569	746
Held to maturity, Due after 1 year through 5, Fair Value	2,925	2,688
Held to maturity, Due after 5 years through 10 years, Fair Value	4,400	4,756
Held to maturity, Due after 10 years, Fair Value	2,887	3,542
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost	10,989	11,611
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Fair Value	10,781	11,732
Held to maturity, Mortgage backed securities, Fair Value	2,503	2,742
Held to maturity, Fair Value	$ 13,284	$ 14,474