Fair Value Measurements (Assets Measured At Fair Value Using Significant Unobservable Inputs) (Detail) - USD ($) $ in Millions		3 Months Ended				9 Months Ended
		Sep. 30, 2020		Sep. 30, 2019		Sep. 30, 2020		Sep. 30, 2019		Jun. 30, 2020		Dec. 31, 2019		Jun. 30, 2019		Dec. 31, 2018
Level 3 | Non-U.S.
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance- Beginning of Period, Assets		$ 469		$ 371		$ 449		$ 345
Transfers Into Level 3, Asset		0		0		0		3
Transfers out of Level 3, Assets		0				(16)		(15)
Asset, Net realized Gain (Loss) Included in Other Comprehensive Income (Loss)		21		(8)		1		(2)
Net Realized Gains/ (Losses), Assets		1		0		(2)		(1)
Purchases, Assets		41		68		190		164
Sales, Assets		(19)		(35)		(81)		(54)
Settlements, Assets		(19)		(3)		(47)		(47)
Balance-End of Period, Assets		494		393		494		393
Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss)		0		0		0		0
Level 3 | Corporate and asset-backed securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance- Beginning of Period, Assets		1,369		1,359		1,451		1,299
Transfers Into Level 3, Asset		1		1		92		16
Transfers out of Level 3, Assets		(1)				(73)		0
Asset, Net realized Gain (Loss) Included in Other Comprehensive Income (Loss)		13		(4)		(31)		1
Net Realized Gains/ (Losses), Assets		3		0		(23)		0
Purchases, Assets		194		176		416		425
Sales, Assets		(80)		(18)		(147)		(91)
Settlements, Assets		(54)		(64)		(240)		(200)
Balance-End of Period, Assets		1,445		1,450		1,445		1,450
Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss)		3		0		(6)		(1)
Level 3 | Mortgage-backed securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance- Beginning of Period, Assets		60		76		60		61
Transfers Into Level 3, Asset		0		0		0		0
Transfers out of Level 3, Assets		0				0		0
Asset, Net realized Gain (Loss) Included in Other Comprehensive Income (Loss)		0		0		0		0
Net Realized Gains/ (Losses), Assets		0		0		0		0
Purchases, Assets		2		1		2		19
Sales, Assets		0		0		0		(1)
Settlements, Assets		(1)		0		(1)		(2)
Balance-End of Period, Assets		61		77		61		77
Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss)		0		0		0		0
Level 3 | Equity Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss), OCI		0				0
Balance- Beginning of Period, Assets		64		56		69		57
Transfers Into Level 3, Asset		0		0		0		0
Transfers out of Level 3, Assets		0				0		0
Asset, Net realized Gain (Loss) Included in Other Comprehensive Income (Loss)		0		(1)		0		1
Net Realized Gains/ (Losses), Assets		2		(1)		(1)		(4)
Purchases, Assets		3		5		14		19
Sales, Assets		(3)		(3)		(16)		(17)
Settlements, Assets		0		0		0		0
Balance-End of Period, Assets		66		56		66		56
Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss)		2		(1)		1		(3)
Level 3 | Short-term Investments [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss), OCI		(1)				(1)
Balance- Beginning of Period, Assets		2		4		6		1
Transfers Into Level 3, Asset		0		0		0		0
Transfers out of Level 3, Assets		0				0		0
Asset, Net realized Gain (Loss) Included in Other Comprehensive Income (Loss)		(1)		0		(1)		0
Net Realized Gains/ (Losses), Assets		0		0		0		0
Purchases, Assets		7		2		9		6
Sales, Assets		0		0		0		0
Settlements, Assets		(1)		0		(7)		(1)
Balance-End of Period, Assets		7		6		7		6
Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss)		0		0		0		0
Level 3 | Other Long-term Investments [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss), OCI		0				0
Balance- Beginning of Period, Assets		10		11		10		11
Transfers Into Level 3, Asset		0		0		0		0
Transfers out of Level 3, Assets		0				0		0
Asset, Net realized Gain (Loss) Included in Other Comprehensive Income (Loss)		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		(1)		0		(1)
Balance-End of Period, Assets		10		10		10		10
Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss)		0		0		0		0
Available-for-sale Securities [Member] | Level 3 | Non-U.S.
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss), OCI		20				0
Available-for-sale Securities [Member] | Level 3 | Corporate and asset-backed securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss), OCI		12				(25)
Available-for-sale Securities [Member] | Level 3 | Mortgage-backed securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss), OCI		0				0
Guaranteed Minimum Income Benefit [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability Value		882		509		882		509		$ 928		$ 456		$ 403		$ 452
Guaranteed Minimum Income Benefit [Member] | Level 3
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Liability, Recurring Basis, Still Held, Unrealized Gain (Loss), OCI		0				0
Guaranteed Minimum Income Benefit [Member] | Fair Value, Recurring [Member] | Level 3
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability Value	[2]	882	[1]			882	[1]					456	[3]
Guaranteed Minimum Income Benefit [Member] | Guarantees [Member] | Level 3
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability Value		882	[4],[5]	509	[5]	882	[4],[5]	509	[5]	$ 928	[4]	$ 456		$ 403	[5]	$ 452	[5]
Transfers into level 3, liability		0		0		0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Other Comprehensive Income (Loss)		0		0		0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Earnings		(46)	[4]	106	[5]	426		57	[5]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Purchases		0		0		0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Sales		0		0		0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Settlements		0		0		0		0
Fair Value, Liability, Recurring Basis, Still Held, Unrealized Gain (Loss)		(46)	[4]	$ 106	[5]	426		57	[5]
Transfers out of Level 3, Liabilities		$ 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. Excluded from the table above is the portion of the GLB derivative liability classified as Future policy benefits in the Consolidated balance sheets.

[2] The weighted average lapse and annuitization rates are determined by weighting each treaty's rates by the GLB contracts fair value.

[3] Our GLB reinsurance product meets the definition of a derivative instrument for accounting purposes and is accordingly carried at fair value. Excluded from the table above is the portion of the GLB derivative liability classified as Future policy benefits in the Consolidated balance sheets.

[4] Our GLB reinsurance product meets the definition of a derivative instrument for accounting purposes and is accordingly carried at fair value. Excluded from the table above is the portion of the GLB derivative liability classified as Future policy benefits in the Consolidated balance sheets. The liability for GLB reinsurance was $1,318 million at September 30, 2020, and $1,372 million at June 30, 2020, which includes a fair value derivative adjustment of $882 million and $928 million, respectivel

[5] Our GLB reinsurance product meets the definition of a derivative instrument for accounting purposes and is accordingly carried at fair value. Excluded from the table above is the portion of the GLB derivative liability classified as Future policy benefits in the Consolidated balance sheets. The liability for GLB reinsurance was $935 million at September 30, 2019, and $815 million at June 30, 2019, which includes a fair value derivative adjustment of $509 million and $403 million, respectively