Fair Value Measurements (Assets Measured At Fair Value Using Significant Unobservable Inputs) (Detail) - USD ($) $ in Millions		3 Months Ended				6 Months Ended
		Jun. 30, 2020		Jun. 30, 2019		Jun. 30, 2020		Jun. 30, 2019		Mar. 31, 2020		Dec. 31, 2019		Mar. 31, 2019		Dec. 31, 2018
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Transfers Into Level 3, Asset						$ 0		$ 0
Level 3 | Non-U.S.
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance- Beginning of Period, Assets		$ 465		$ 360		449		345
Transfers Into Level 3, Asset				0		0		3
Transfers out of Level 3, Assets		(13)				(16)		(15)
Asset, Net realized Gain (Loss) Included in Other Comprehensive Income (Loss)		(6)		0		(20)		6
Net Realized Gains/ (Losses), Assets		(1)		0		(3)		(1)
Purchases, Assets		67		43		149		96
Sales, Assets		(16)		(14)		(62)		(19)
Settlements, Assets		(27)		(18)		(28)		(44)
Balance-End of Period, Assets		469		371		469		371
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		1,502		1,342		1,451		1,299
Transfers Into Level 3, Asset				10		91		15
Transfers out of Level 3, Assets		(71)				(72)		0
Asset, Net realized Gain (Loss) Included in Other Comprehensive Income (Loss)		1		1		(44)		5
Net Realized Gains/ (Losses), Assets		(13)		(1)		(26)		0
Purchases, Assets		83		121		222		249
Sales, Assets		(48)		(36)		(67)		(73)
Settlements, Assets		(85)		(78)		(186)		(136)
Balance-End of Period, Assets		1,369		1,359		1,369		1,359
Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss)		5		(1)		(9)		(1)
Level 3 | Mortgage-backed securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance- Beginning of Period, Assets		60		78		60		61
Transfers Into Level 3, Asset				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		18
Sales, Assets		0		(1)		0		(1)
Settlements, Assets		0		(1)		0		(2)
Balance-End of Period, Assets		60		76		60		76
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		67		55		69		57
Transfers Into Level 3, Asset				0
Transfers out of Level 3, Assets		0				0		0
Asset, Net realized Gain (Loss) Included in Other Comprehensive Income (Loss)		(1)		1		0		2
Net Realized Gains/ (Losses), Assets		(1)		(1)		(3)		(3)
Purchases, Assets		8		5		11		14
Sales, Assets		(9)		(4)		(13)		(14)
Settlements, Assets		0		0		0		0
Balance-End of Period, Assets		64		56		64		56
Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss)		1		(1)		(1)		(2)
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		0				0
Balance- Beginning of Period, Assets		1		0		6		1
Transfers Into Level 3, Asset				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		1		4		2		4
Sales, Assets		0		0		0		0
Settlements, Assets		0		0		(6)		(1)
Balance-End of Period, Assets		2		4		2		4
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
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		0		0		0
Balance-End of Period, Assets		10		11		10		11
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		(5)				(20)
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		7				(37)
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		928		403		928		403		$ 1,141		$ 456		$ 338		$ 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	[1]	928				928						456	[2]
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		928	[3],[4]	403	[4]	928	[3],[4]	403	[4]	$ 1,141	[3]	$ 456		$ 338	[4]	$ 452	[4]
Transfers into level 3, liability				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		(213)	[3]	65	[4]	472		(49)	[4]
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)		(213)	[3]	$ 65	[4]	472		(49)	[4]
Transfers out of Level 3, Liabilities		$ 0				$ 0		$ 0

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

[2] 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.

[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. The liability for GLB reinsurance was $1,372 million at June 30, 2020, and $1,591 million at March 31, 2020, which includes a fair value derivative adjustment of $928 million and $1,141 million, respectivel

[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 $815 million at June 30, 2019, and $741 million at March 31, 2019, which includes a fair value derivative adjustment of $403 million and $338 million, respectively