Fair Value Measurements (Schedule Of Significant Unobservable Inputs Used In Level 3 Liability Valuations) (Detail) - USD ($) $ in Millions		6 Months Ended
		Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019		Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value Measurements, Valuation Processes, Description		Actuarial model
GLB
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability Value		$ 928	$ 1,141	$ 456		$ 403	$ 338	$ 452
Guaranteed Benefit Liability, Net		$ 1,372	$ 1,591	897		$ 815	$ 741	$ 861
Weighted Average [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Long-Duration Contracts, Assumptions by Product and Guarantee, Lapse Rate	[1]	4.60%
Significant Unobservable Inputs Annuitization Rate	[1]	4.10%
Minimum [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Long-Duration Contracts, Assumptions by Product and Guarantee, Lapse Rate		3.00%
Significant Unobservable Inputs Annuitization Rate		0.00%
Maximum [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Long-Duration Contracts, Assumptions by Product and Guarantee, Lapse Rate		34.00%
Significant Unobservable Inputs Annuitization Rate		52.00%
Level 3 | Fair Value, Recurring [Member] | GLB
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability Value	[1]	$ 928		$ 456	[2]

[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.