Fair Value Measurements (Schedule Of Significant Unobservable Inputs Used In Level 3 Liability Valuations) (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015		Dec. 31, 2014
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Valuation Technique	[1]	Actuarial model
Guaranteed Minimum Income Benefit
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Purchases		$ 0	[2]	$ 0	[3]	$ 0	[4]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Liability, Transfers out of Level 3				0	[3]	0	[4]
Fair Value, Measurement with Unobservable Inputs Reconciliations, Recurring Basis, Liability Value		204	[2]	559	[2],[3]	609	[3],[4]	$ 406	[4]
Level 3 | Guaranteed Minimum Income Benefit
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliations, Recurring Basis, Liability Value		$ 204	[1]	559
Minimum
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Long-Duration Contracts, Assumptions by Product and Guarantee, Lapse Rate	[1]	3.00%
Annuitization rate	[1]	0.00%
Maximum
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Long-Duration Contracts, Assumptions by Product and Guarantee, Lapse Rate	[1]	33.00%
Annuitization rate	[1]	100.00%
Short-term Investments [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements		$ 41		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3				50
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Other Comprehensive Income (Loss)		0		0
Other Derivative Instruments Fair Value [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements				0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Purchases		0		2		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Liability, Transfers out of Level 3		9
Fair Value, Measurement with Unobservable Inputs Reconciliations, Recurring Basis, Liability Value		$ 2		$ 13		$ 6		$ 4

[1] Discussion of the most significant inputs used in the fair value measurement of GLB and the sensitivity of those assumptions is included within Note 4 a) Guaranteed living benefits.

[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. Refer to Note 5 c) for additional information.

[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 $853 million at December 31, 2016 and $888 million at December 31, 2015, which includes a fair value derivative adjustment of $559 million and $609 million, respectively.

[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 $888 million at December 31, 2015 and $663 million at December 31, 2014, which includes a fair value derivative adjustment of $609 million and $406 million, respectively.