Fair Value Measurements (Financial Instruments Measured At Fair Value On Recurring Basis) (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017		Mar. 31, 2016		Dec. 31, 2016		Dec. 31, 2015	[2]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale, Fair Value	$ 80,806				$ 80,115
Equity securities, at fair value	835				814
Other Investments	4,551				4,519
Securities lending collateral	1,071				1,092
Fair Value, Level 1 to Level 2 transfers, Amount	0		$ 0
Fair Value, Level 2 to Level 1 Transfers, Amount	0		0
Investment Funds Limited Partnerships Partially Owned Investment Companies Fair Value [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Other Investments	3,594				3,626
Other Investments [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Other Investments	20				25
Fair Value, Measurements, Recurring [Member] | Estimate of Fair Value Measurement [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale, Fair Value	80,806				80,115
Equity securities, at fair value	835				814
Short-term investments	2,780				3,002
Other Investments	937				868
Securities lending collateral	1,071				1,092
Investment derivative instruments, assets	15				31
Other Derivative Instruments Fair Value	8				3
Separate Account Assets	2,067				1,879
Total assets measured at fair value	88,519				87,804
Investment derivative instruments, liabilities	30				54
Other derivative instruments, liability	11				13
Liabilities, Fair Value Disclosure, Recurring	507				626
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale, Fair Value	862				800
Equity securities, at fair value	41				41
Short-term investments	21				25
Other Investments	232				225
Total assets measured at fair value	1,156				1,091
Other derivative instruments, liability	11				13
Liabilities, Fair Value Disclosure, Recurring	477				572
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale, Fair Value	2,222				2,175
Equity securities, at fair value	794				773
Short-term investments	1,548				1,757
Other Investments	425				384
Investment derivative instruments, assets	15				31
Other Derivative Instruments Fair Value	8				3
Separate Account Assets	1,970				1,784
Total assets measured at fair value	6,982				6,907
Investment derivative instruments, liabilities	30				54
Liabilities, Fair Value Disclosure, Recurring	30				54
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale, Fair Value	77,722				77,140
Short-term investments	1,211				1,220
Other Investments	280				259
Securities lending collateral	1,071				1,092
Separate Account Assets	97				95
Total assets measured at fair value	80,381				79,806
Fair Value, Measurements, Recurring [Member] | U.S. Treasury And Agency [Member] | Estimate of Fair Value Measurement [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale, Fair Value	2,899				2,870
Fair Value, Measurements, Recurring [Member] | U.S. Treasury And Agency [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale, Fair Value	2,222				2,175
Fair Value, Measurements, Recurring [Member] | U.S. Treasury And Agency [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale, Fair Value	677				695
Fair Value, Measurements, Recurring [Member] | Foreign [Member] | Estimate of Fair Value Measurement [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale, Fair Value	21,367				21,440
Fair Value, Measurements, Recurring [Member] | Foreign [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale, Fair Value	80				74
Fair Value, Measurements, Recurring [Member] | Foreign [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale, Fair Value	21,287				21,366
Fair Value, Measurements, Recurring [Member] | Corporate [Member] | Estimate of Fair Value Measurement [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale, Fair Value	24,842				24,149
Fair Value, Measurements, Recurring [Member] | Corporate [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale, Fair Value	737				681
Fair Value, Measurements, Recurring [Member] | Corporate [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale, Fair Value	24,105				23,468
Fair Value, Measurements, Recurring [Member] | Collateralized Mortgage Backed Securities [Member] | Estimate of Fair Value Measurement [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale, Fair Value	14,146				14,007
Fair Value, Measurements, Recurring [Member] | Collateralized Mortgage Backed Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale, Fair Value	45				45
Fair Value, Measurements, Recurring [Member] | Collateralized Mortgage Backed Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale, Fair Value	14,101				13,962
Fair Value, Measurements, Recurring [Member] | States, Municipalities, And Political Subdivisions [Member] | Estimate of Fair Value Measurement [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale, Fair Value	17,552				17,649
Fair Value, Measurements, Recurring [Member] | States, Municipalities, And Political Subdivisions [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale, Fair Value	17,552				17,649
Guaranteed Minimum Income Benefit [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliations, Recurring Basis, Liability Value	466	[1]	$ 839	[1],[2]	559	[1]	$ 609
Guaranteed Minimum Income Benefit [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliations, Recurring Basis, Liability Value					559
Guaranteed Minimum Income Benefit [Member] | Fair Value, Measurements, Recurring [Member] | Estimate of Fair Value Measurement [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliations, Recurring Basis, Liability Value	466	[3]			559
Guaranteed Minimum Income Benefit [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliations, Recurring Basis, Liability Value	$ 466	[4]			$ 559

[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. The liability for GLB reinsurance was $774 million at March 31, 2017, and $853 million at December 31, 2016, which includes a fair value derivative adjustment of $466 million and $559 million, respectively.

[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 $1.1 billion at March 31, 2016, and $888 million at December 31, 2015, which includes a fair value derivative adjustment of $839 million and $609 million, respectively.(2) Includes acquired invested assets as a result of the Chubb Corp acquisition.

[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] 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.