Investments (Net Realized Gains (Losses) And Losses Included In Net Realized Gains (Losses) And Other Comprehensive Income) (Detail) - USD ($) $ in Millions	3 Months Ended							12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Gain (Loss) on Securities [Line Items]
Other-than-temporary impairment (OTTI) losses gross								$ (52)	$ (46)	$ (111)
OTTI on fixed maturities, net									(45)	(103)
OTTI on Fixed Maturities								49
Foreign exchange gains( losses)								131	36	118
Fair Value adjustment on insurance derivative								(248)	364	53
Derivative, Gain (Loss) on Derivative, Net								(330)	87	(126)
Net Realized Gain (Loss)	$ (687)	$ 19	$ 18	$ (2)				(652)
Net Realized Investment Gains (Losses) including OTTI					$ (10)	$ 101	$ (7)		84	(145)
Unrealized Gain (Loss) on Investments								(1,699)	392	184
Other Comprehensive Income (Loss), Securities, Available-for-sale, Tax								297	(241)	100
Other derivative instruments
Gain (Loss) on Securities [Line Items]
Derivative, Gain (Loss) on Derivative, Net								(3)	(5)	(10)
Investment and embedded derivative instruments
Gain (Loss) on Securities [Line Items]
Derivative, Gain (Loss) on Derivative, Net								(75)	(11)	(33)
S&P Options and Futures
Gain (Loss) on Securities [Line Items]
Derivative, Gain (Loss) on Derivative, Net								(4)	(261)	(136)
Equity Securities [Member]
Gain (Loss) on Securities [Line Items]
Other-than-temporary impairment (OTTI) losses gross								0	(10)	(8)
Equity Securities, FV-NI, Realized Gain								74
Equity Securities - Gross Realized Gains Excluding OTTI									28	65
Equity Securities, FV-NI, Realized Loss								133
Equity Securities - Gross realized losses excluding OTTI									(2)	(13)
Equity Securities, FV-NI, Realized Gain (Loss)								(59)
Total net realized gains (losses) (includes $(302), $(15), and $(119) reclassified from AOCI)									16	44
Unrealized Gain (Loss) on Investments								0	88	52
Fixed maturities held to maturity
Gain (Loss) on Securities [Line Items]
Unrealized Gain (Loss) on Investments								(38)	18	(59)
Other Investments [Member]
Gain (Loss) on Securities [Line Items]
Other-than-temporary impairment (OTTI) losses gross								0	(12)	(14)
Realized Investment Gains (Losses)								(5)	0	0
Available-for-sale Securities [Member]
Gain (Loss) on Securities [Line Items]
Unrealized Gain (Loss) on Investments								(1,958)	519	142
Debt Securities [Member]
Gain (Loss) on Securities [Line Items]
Other-than-temporary impairment (OTTI) losses gross								(52)	(24)	(89)
OTTI on fixed maturities recognized in OCI (pre-tax)								3	1	8
OTTI on fixed maturities, net									(23)	(81)
Gross realized gains excluding OTTI									149	183
Gross realized losses excluding OTTI									157	265
OTTI on Fixed Maturities								49
Total fixed maturities									(31)	(163)
Fixed Maturities [Member]
Gain (Loss) on Securities [Line Items]
Debt Securities, Available-for-sale, Realized Gain (Loss), Excluding Other-than-temporary Impairment								334
Debt Securities, Available-for-sale, Realized Loss, Excluding Other-than-temporary Impairment								(587)
Debt Securities, Available-for-sale, Realized Gain (Loss)								(302)
Other [Member]
Gain (Loss) on Securities [Line Items]
Gain (Loss) on Sale of Other Investments								(87)	(12)	(4)
Unrealized Gain (Loss) on Investments								$ 0	$ 8	$ (51)