Investments (Schedule Of Amortized Cost And Fair Value Of Held-to-Maturity And Related Other-Than-Temporary Impairment Recognized In Accumulated Other Comprehensive Income) (Detail) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Schedule of Held-to-maturity Securities [Line Items]
Fixed maturities held to maturity, at amortized cost (fair value – $14,474 and $10,670)	$ 14,335	$ 10,644
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain	179	148
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	(40)	(122)
Held to maturity, Fair Value	14,474	10,670
Held to maturity, OTTI recognized in AOCI		0
U.S. Treasury and agency
Schedule of Held-to-maturity Securities [Line Items]
Fixed maturities held to maturity, at amortized cost (fair value – $14,474 and $10,670)	908	655
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain	12	9
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	(5)	(3)
Held to maturity, Fair Value	915	661
Held to maturity, OTTI recognized in AOCI	0	0
Foreign
Schedule of Held-to-maturity Securities [Line Items]
Fixed maturities held to maturity, at amortized cost (fair value – $14,474 and $10,670)	1,738	640
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain	27	28
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	(8)	(1)
Held to maturity, Fair Value	1,757	667
Held to maturity, OTTI recognized in AOCI	0	0
Corporate securities
Schedule of Held-to-maturity Securities [Line Items]
Fixed maturities held to maturity, at amortized cost (fair value – $14,474 and $10,670)	3,159	2,771
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain	67	50
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	(7)	(26)
Held to maturity, Fair Value	3,219	2,795
Held to maturity, OTTI recognized in AOCI	0	0
Mortgage backed-securities
Schedule of Held-to-maturity Securities [Line Items]
Fixed maturities held to maturity, at amortized cost (fair value – $14,474 and $10,670)	2,724	1,393
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain	23	35
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	(5)	0
Held to maturity, Fair Value	2,742	1,428
Held to maturity, OTTI recognized in AOCI	0	0
States, municipalities, and political subdivisions
Schedule of Held-to-maturity Securities [Line Items]
Fixed maturities held to maturity, at amortized cost (fair value – $14,474 and $10,670)	5,806	5,185
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain	50	26
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	(15)	(92)
Held to maturity, Fair Value	5,841	5,119
Held to maturity, OTTI recognized in AOCI	$ 0	$ 0