Investments (Schedule Of Amortized Cost And Fair Value Of HTM Fixed Maturities And Related OTTI Recognized In Accumulated Other Comprehensive Income) (Detail) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020	Dec. 31, 2019
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-maturity	$ 11,175	$ 11,697
Debt Securities, Held-to-maturity, Allowance for Credit Loss	(43)	(44)	$ (45)	$ 0
Debt securities, held to maturity, net carrying value	11,132	11,653
Held-to-maturity, Gross Unrealized Appreciation	621	859
Held-to-maturity, Gross Unrealized Depreciation	(1)	(2)
Held to maturity, at Fair Value	11,752	12,510
U.S. Treasury / Agency
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-maturity	1,158	1,392
Debt Securities, Held-to-maturity, Allowance for Credit Loss	0	0
Debt securities, held to maturity, net carrying value	1,158	1,392
Held-to-maturity, Gross Unrealized Appreciation	39	60
Held-to-maturity, Gross Unrealized Depreciation	0	0
Held to maturity, at Fair Value	1,197	1,452
Non-U.S.
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-maturity	1,276	1,295
Debt Securities, Held-to-maturity, Allowance for Credit Loss	(6)	(7)
Debt securities, held to maturity, net carrying value	1,270	1,288
Held-to-maturity, Gross Unrealized Appreciation	82	118
Held-to-maturity, Gross Unrealized Depreciation	(1)	(1)
Held to maturity, at Fair Value	1,351	1,405
Corporate and asset-backed securities
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-maturity	2,163	2,185
Debt Securities, Held-to-maturity, Allowance for Credit Loss	(35)	(35)
Debt securities, held to maturity, net carrying value	2,128	2,150
Held-to-maturity, Gross Unrealized Appreciation	183	288
Held-to-maturity, Gross Unrealized Depreciation	0	0
Held to maturity, at Fair Value	2,311	2,438
Mortgage-backed securities
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-maturity	1,888	2,000
Debt Securities, Held-to-maturity, Allowance for Credit Loss	(1)	(1)
Debt securities, held to maturity, net carrying value	1,887	1,999
Held-to-maturity, Gross Unrealized Appreciation	110	148
Held-to-maturity, Gross Unrealized Depreciation	0	(1)
Held to maturity, at Fair Value	1,997	2,146
Municipal
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-maturity	4,690	4,825
Debt Securities, Held-to-maturity, Allowance for Credit Loss	(1)	(1)
Debt securities, held to maturity, net carrying value	4,689	4,824
Held-to-maturity, Gross Unrealized Appreciation	207	245
Held-to-maturity, Gross Unrealized Depreciation	0	0
Held to maturity, at Fair Value	$ 4,896	$ 5,069