Fair Value Measurements (Assets and Liabilities, Measured At Fair Value Using Significant Unobservable Inputs) (Detail) - Level 3 - USD ($) $ in Millions	3 Months Ended				9 Months Ended
	Sep. 30, 2021		Sep. 30, 2020		Sep. 30, 2021		Sep. 30, 2020
Equity Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance- Beginning of Period, Assets	$ 78		$ 64		$ 73		$ 69
Transfers Into Level 3, Asset	0				0		0
Transfers out of Level 3, Assets	0		0		0		0
Change in Net Unrealized Gains (Losses) included in OCI, Assets	0		0		0		0
Net Realized Gains/ (Losses), Assets	1		2		8		(1)
Purchases, Assets	4		3		11		14
Sales, Assets	(4)		(3)		(13)		(16)
Settlements, Assets	0		0		0		0
Other, Assets	0		0		0		0
Balance-End of Period, Assets	79		66		79		66
Net Realized Gains/Losses Attributable to Changes in Fair Value at the Balance Sheet Date, Assets	(1)		2		5		1
Change in Net Unrealized Gains/Losses included in OCI at the Balance Sheet Date, Assets	0		0		0		0
Short-term Investments [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance- Beginning of Period, Assets	3		2		5		6
Transfers Into Level 3, Asset	0				0		0
Transfers out of Level 3, Assets	0		0		0		0
Change in Net Unrealized Gains (Losses) included in OCI, Assets	0		(1)		0		(1)
Net Realized Gains/ (Losses), Assets	0		0		0		0
Purchases, Assets	7		7		10		9
Sales, Assets	0		0		0		0
Settlements, Assets	0		(1)		(5)		(7)
Other, Assets	0		0		0		0
Balance-End of Period, Assets	10		7		10		7
Net Realized Gains/Losses Attributable to Changes in Fair Value at the Balance Sheet Date, Assets	0		0		0		0
Change in Net Unrealized Gains/Losses included in OCI at the Balance Sheet Date, Assets	0		(1)		0		(1)
Other Investments [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance- Beginning of Period, Assets	10		10		10		10
Transfers Into Level 3, Asset	0				0		0
Transfers out of Level 3, Assets	(10)		0		(10)		0
Change in Net Unrealized Gains (Losses) included in OCI, Assets	0		0		0		0
Net Realized Gains/ (Losses), Assets	0		0		0		0
Purchases, Assets	0		0		0		0
Sales, Assets	0		0		0		0
Settlements, Assets	0		0		0		0
Other, Assets	0		0		0		0
Balance-End of Period, Assets	0		10		0		10
Net Realized Gains/Losses Attributable to Changes in Fair Value at the Balance Sheet Date, Assets	0		0		0		0
Change in Net Unrealized Gains/Losses included in OCI at the Balance Sheet Date, Assets	0		0		0		0
Available-for-sale Securities [Member] | Non-U.S.
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance- Beginning of Period, Assets	642		469		546		449
Transfers Into Level 3, Asset	22				22		0
Transfers out of Level 3, Assets	0		0		(10)		(16)
Change in Net Unrealized Gains (Losses) included in OCI, Assets	(15)		21		(2)		1
Net Realized Gains/ (Losses), Assets	(3)		1		0		(2)
Purchases, Assets	60		41		235		190
Sales, Assets	(19)		(19)		(35)		(81)
Settlements, Assets	(27)		(19)		(96)		(47)
Other, Assets	0		0		0		0
Balance-End of Period, Assets	660		494		660		494
Net Realized Gains/Losses Attributable to Changes in Fair Value at the Balance Sheet Date, Assets	0		0		0		0
Change in Net Unrealized Gains/Losses included in OCI at the Balance Sheet Date, Assets	(15)		20		2		0
Available-for-sale Securities [Member] | Corporate and asset-backed securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance- Beginning of Period, Assets	1,688		1,369		1,573		1,451
Transfers Into Level 3, Asset	45				91		92
Transfers out of Level 3, Assets	0		(1)		(3)		(73)
Change in Net Unrealized Gains (Losses) included in OCI, Assets	2		(13)		14		(31)
Net Realized Gains/ (Losses), Assets	0		3		3		(23)
Purchases, Assets	272		194		681		416
Sales, Assets	(13)		(80)		(88)		(147)
Settlements, Assets	(135)		(54)		(412)		(240)
Other, Assets	0		0		0		0
Balance-End of Period, Assets	1,859		1,445		1,859		1,445
Net Realized Gains/Losses Attributable to Changes in Fair Value at the Balance Sheet Date, Assets	0		3		3		(6)
Change in Net Unrealized Gains/Losses included in OCI at the Balance Sheet Date, Assets	0		12		17		(25)
Available-for-sale Securities [Member] | Mortgage-backed securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance- Beginning of Period, Assets	47		60		60		60
Transfers Into Level 3, Asset	0				0		0
Transfers out of Level 3, Assets	0		0		0		0
Change in Net Unrealized Gains (Losses) included in OCI, Assets	0		0		0		0
Net Realized Gains/ (Losses), Assets	0		0		0		0
Purchases, Assets	17		2		18		2
Sales, Assets	0		0		(1)		0
Settlements, Assets	(11)		(1)		(24)		(1)
Other, Assets	0		0		0		0
Balance-End of Period, Assets	53		61		53		61
Net Realized Gains/Losses Attributable to Changes in Fair Value at the Balance Sheet Date, Assets	0		0		0		0
Change in Net Unrealized Gains/Losses included in OCI at the Balance Sheet Date, Assets	0		0		0		0
Guaranteed Minimum Income Benefit [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance - Beginning of Period, Liabilities	760	[1]	1,372	[2]	1,089		897
Transfers into level 3, liability	0				0		0
Transfers out of Level 3, Liabilities	0		0		0		0
Change in Net Unrealized Gains (losses) included in OCI, Liabilities	0		0		0		0
Net Realized Gains/(Losses), Liabilities	59	[1]	(46)	[2]	(252)		426
Purchases, Liabilities	0		0		0		0
Sales, Liabilities	0		0		0		0
Settlements, Liabilities	0		0		0		0
Other, Liabilities	(1)		(8)		(19)		(5)
Balance - End of Period, Liabilities	818	[1]	1,318	[2]	818	[1]	1,318	[2]
Net Realized Gains/Losses Attributable to Changes in Fair Value at the Balance Sheet Date, Liabilities	59	[1]	(46)	[2]	(252)		426
Change in Net Unrealized Gains/Losses included in OCI at the Balance Sheet Date, Liabilities	$ 0		$ 0		$ 0		$ 0

[1] Our GLB reinsurance product meets the definition of a derivative instrument for accounting purposes and is accordingly carried at fair value.

[2] Our GLB reinsurance product meets the definition of a derivative instrument for accounting purposes and is accordingly carried at fair value.