Fair Value Measurements (Financial Instruments Measured At Fair Value Using Significant Unobservable Inputs) (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016		Mar. 31, 2015		Dec. 31, 2015	Dec. 31, 2014
Schedule Of Fair Value Measurements [Line Items]
Document Period End Date	Mar. 31, 2016
Equity Securities [Member]
Schedule Of Fair Value Measurements [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3	$ 0		$ 0
Balance- Beginning of Period, Assets	16		2
Transfers out of Level 3, Assets	0
Change in Net Unrealized Gains (Losses) included in OCI, Assets	0		0
Purchases, Assets	13		0
Sales, Assets	0		0
Settlements, Assets	0		0
Balance-End of Period, Assets	29		2
Net Realized Gains/Losses Attributable to Changes in Fair Value at the Balance Sheet Date, Assets	0		0
Equity Securities [Member] | Gain (Loss) on Investments [Member]
Schedule Of Fair Value Measurements [Line Items]
Net Realized Gains/Losses, Assets	0		0
Other Long-term Investments [Member]
Schedule Of Fair Value Measurements [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3	0		0
Balance- Beginning of Period, Assets	212		204
Transfers out of Level 3, Assets	0
Change in Net Unrealized Gains (Losses) included in OCI, Assets	0		(2)
Purchases, Assets	6		9
Sales, Assets	0		0
Settlements, Assets	(7)		(3)
Balance-End of Period, Assets	211		208
Net Realized Gains/Losses Attributable to Changes in Fair Value at the Balance Sheet Date, Assets	0		0
Other Long-term Investments [Member] | Gain (Loss) on Investments [Member]
Schedule Of Fair Value Measurements [Line Items]
Net Realized Gains/Losses, Assets	0		0
Other Derivative Instruments Fair Value [Member]
Schedule Of Fair Value Measurements [Line Items]
Balance - Beginning of Period, Liabilities	6		4
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3			0
Change in Net Unrealized Gains (Losses) included in OCI, Assets	0		0
Purchases, Assets			0
Sales, Assets			0
Settlements, Assets	0		0
Balance-End of Period, Assets	10		4
Net Realized Gains/Losses Attributable to Changes in Fair Value at the Balance Sheet Date, Liabilities	2		0
Other Derivative Instruments Fair Value [Member] | Gain (Loss) on Investments [Member]
Schedule Of Fair Value Measurements [Line Items]
Net Realized Gains/Losses, Liabilities	2		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Purchases	2
Available-for-sale Securities [Member] | Foreign [Member]
Schedule Of Fair Value Measurements [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3	6		0
Balance- Beginning of Period, Assets	57		22
Transfers out of Level 3, Assets	(2)
Change in Net Unrealized Gains (Losses) included in OCI, Assets	6		0
Purchases, Assets	5		1
Sales, Assets	(1)		(1)
Settlements, Assets	(4)		0
Balance-End of Period, Assets	62		22
Net Realized Gains/Losses Attributable to Changes in Fair Value at the Balance Sheet Date, Assets	(4)		0
Available-for-sale Securities [Member] | Foreign [Member] | Gain (Loss) on Investments [Member]
Schedule Of Fair Value Measurements [Line Items]
Net Realized Gains/Losses, Assets	(5)		0
Available-for-sale Securities [Member] | Corporate [Member]
Schedule Of Fair Value Measurements [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3	16		1
Balance- Beginning of Period, Assets	174		187
Transfers out of Level 3, Assets	0
Change in Net Unrealized Gains (Losses) included in OCI, Assets	2		3
Purchases, Assets	93		8
Sales, Assets	(14)		(3)
Settlements, Assets	(4)		(26)
Balance-End of Period, Assets	261		167
Net Realized Gains/Losses Attributable to Changes in Fair Value at the Balance Sheet Date, Assets	(7)		(2)
Available-for-sale Securities [Member] | Corporate [Member] | Gain (Loss) on Investments [Member]
Schedule Of Fair Value Measurements [Line Items]
Net Realized Gains/Losses, Assets	(6)		(3)
Available-for-sale Securities [Member] | Collateralized Mortgage Backed Securities [Member]
Schedule Of Fair Value Measurements [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3	0		0
Balance- Beginning of Period, Assets	53		15
Transfers out of Level 3, Assets	0
Change in Net Unrealized Gains (Losses) included in OCI, Assets	0		0
Purchases, Assets	0		18
Sales, Assets	(5)		0
Settlements, Assets	0		0
Balance-End of Period, Assets	48		33
Net Realized Gains/Losses Attributable to Changes in Fair Value at the Balance Sheet Date, Assets	0		0
Available-for-sale Securities [Member] | Collateralized Mortgage Backed Securities [Member] | Gain (Loss) on Investments [Member]
Schedule Of Fair Value Measurements [Line Items]
Net Realized Gains/Losses, Assets	0		0
Guaranteed Living Benefit [Member]
Schedule Of Fair Value Measurements [Line Items]
Balance - Beginning of Period, Liabilities	609	[1]	406	[2]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3	0
Transfers out of Level 3, Assets	0
Change in Net Unrealized Gains (Losses) included in OCI, Assets	0
Purchases, Assets	0
Sales, Assets	0
Settlements, Assets	0
Balance - End of Period, Liabilities	839	[1]	451	[2]
Net Realized Gains/Losses Attributable to Changes in Fair Value at the Balance Sheet Date, Liabilities	230		45	[2]
Reported liabilities	1,100		716		$ 888	$ 663
Guaranteed Living Benefit [Member] | Gain (Loss) on Investments [Member]
Schedule Of Fair Value Measurements [Line Items]
Net Realized Gains/Losses, Liabilities	$ 230		$ 45

[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. Refer to Note 5 for additional information.

[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. The liability for GLB reinsurance was $716 million at March 31, 2015, and $663 million at December 31, 2014, which includes a fair value derivative adjustment of $451 million and $406 million, respectively.