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Fair Value Measurements (Financial Instruments Measured At Fair Value On Recurring Basis) (Detail) - USD ($) $ in Millions | Jun. 30, 2017 | Mar. 31, 2017 | [1] | Dec. 31, 2016 | Jun. 30, 2016 | [1],[2] | Mar. 31, 2016 | [2] | Dec. 31, 2015 | [1],[2]
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Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] |  |  |  |  |  |  |  |
Available for sale, Fair Value | $ 81,645 |  |  | $ 80,115 |  |  |  |
Equity securities, at fair value | 856 |  |  | 814 |  |  |  |
Other Investments | 4,685 |  |  | 4,519 |  |  |  |
Securities lending collateral | 1,545 |  |  | 1,092 |  |  |  |
Investment Funds Limited Partnerships Partially Owned Investment Companies Fair Value [Member] |  |  |  |  |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] |  |  |  |  |  |  |  |
Other Investments | 3,711 |  |  | 3,626 |  |  |  |
Other Investments [Member] |  |  |  |  |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] |  |  |  |  |  |  |  |
Other Investments | 19 |  |  | 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 | 81,645 |  |  | 80,115 |  |  |  |
Equity securities, at fair value | 856 |  |  | 814 |  |  |  |
Short-term investments | 2,651 |  |  | 3,002 |  |  |  |
Other Investments | 955 |  |  | 868 |  |  |  |
Securities lending collateral | 1,545 |  |  | 1,092 |  |  |  |
Investment derivative instruments, assets | 12 |  |  | 31 |  |  |  |
Other Derivative Instruments Fair Value | 9 |  |  | 3 |  |  |  |
Separate Account Assets | 2,248 |  |  | 1,879 |  |  |  |
Total assets measured at fair value | 89,921 |  |  | 87,804 |  |  |  |
Investment derivative instruments, liabilities | 35 |  |  | 54 |  |  |  |
Other derivative instruments, liability | 2 |  |  | 13 |  |  |  |
Liabilities, Fair Value Disclosure, Recurring | 394 |  |  | 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 | 877 |  |  | 800 |  |  |  |
Equity securities, at fair value | 39 |  |  | 41 |  |  |  |
Short-term investments | 7 |  |  | 25 |  |  |  |
Other Investments | 243 |  |  | 225 |  |  |  |
Total assets measured at fair value | 1,166 |  |  | 1,091 |  |  |  |
Other derivative instruments, liability | 2 |  |  | 13 |  |  |  |
Liabilities, Fair Value Disclosure, Recurring | 359 |  |  | 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 | 2,486 |  |  | 2,175 |  |  |  |
Equity securities, at fair value | 817 |  |  | 773 |  |  |  |
Short-term investments | 1,421 |  |  | 1,757 |  |  |  |
Other Investments | 430 |  |  | 384 |  |  |  |
Investment derivative instruments, assets | 12 |  |  | 31 |  |  |  |
Other Derivative Instruments Fair Value | 9 |  |  | 3 |  |  |  |
Separate Account Assets | 2,147 |  |  | 1,784 |  |  |  |
Total assets measured at fair value | 7,322 |  |  | 6,907 |  |  |  |
Investment derivative instruments, liabilities | 35 |  |  | 54 |  |  |  |
Liabilities, Fair Value Disclosure, Recurring | 35 |  |  | 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 | 78,282 |  |  | 77,140 |  |  |  |
Short-term investments | 1,223 |  |  | 1,220 |  |  |  |
Other Investments | 282 |  |  | 259 |  |  |  |
Securities lending collateral | 1,545 |  |  | 1,092 |  |  |  |
Separate Account Assets | 101 |  |  | 95 |  |  |  |
Total assets measured at fair value | 81,433 |  |  | 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 | 3,136 |  |  | 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 | 2,486 |  |  | 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 | 650 |  |  | 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 | 21,710 |  |  | 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 | 85 |  |  | 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 | 21,625 |  |  | 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 | 25,364 |  |  | 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 | 747 |  |  | 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 | 24,617 |  |  | 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 | 14,473 |  |  | 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 | 14,428 |  |  | 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 | 16,962 |  |  | 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 | 16,962 |  |  | 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 | 357 | [1] | $ 466 | 559 | [1] | $ 971 | $ 839 | $ 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 | 357 |  |  | 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 | $ 357 | [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 |  |  |  | $ 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 $684 million at June 30, 2017, and $774 million at March 31, 2017, which includes a fair value derivative adjustment of $357 million and $466 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 $1.3 billion at June 30, 2016, and $1.1 billion at March 31, 2016, which includes a fair value derivative adjustment of $971 million and $839 million, respectively. Assets Liabilities Six Months EndedAvailable-for-Sale Debt SecuritiesEquitysecuritiesShort-term investmentsOtherinvestments OtherderivativeinstrumentsGLB(1)June 30, 2017Foreign Corporatesecurities MBS (in millions of U.S. dollars) Balance – beginning of period$74 $681 $45 $41$25$225 $13$559Transfers into Level 3— 57 — ——— —9Transfers out of Level 3— (67) — ——— (9)—Change in Net Unrealized Gains (Losses) included in OCI2 (8) — 1—3 ——Net Realized Gains/Losses1 (1) — ——— (2)(211)Purchases33 221 1 61424 ——Sales(22) (55) (1) (9)—— ——Settlements(3) (81) — —(32)(9) ——Balance – end of period$85 $747 $45 $39$7$243 $2$357Net Realized Gains/Losses Attributable to Changes in Fair Value at the Balance Sheet Date$— $— $— $—$—$— $(2)$(211)(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 $684 million at June 30, 2017, and $853 million at December 31, 2016, which includes a fair value derivative adjustment of $357 million and $559 million, respectively. Assets LiabilitiesSix Months EndedAvailable-for-Sale Debt Securities Equitysecurities Short-term investments Otherinvestments Other derivative instruments GLB(1)June 30, 2016Foreign Corporatesecurities MBS (in millions of U.S. dollars) Balance – beginning of period$57 $174 $53 $16 $— $212 $6 $609Transfers into Level 39 18 — — — — — —Transfers out of Level 3(2) — — — — — — —Change in Net Unrealized Gains (Losses) included in OCI9 11 — (1) — — — —Net Realized Gains/Losses(6) (8) — 1 — — 2 362Purchases (2)32 124 1 23 50 14 2 —Sales(8) (30) (5) (2) — — — —Settlements(4) (8) — — — (10) — —Balance – end of period$87 $281 $49 $37 $50 $216 $10 $971Net Realized Gains/Losses Attributable to Changes in Fair Value at the Balance Sheet Date$(5) $(7) $— $— $— $— $2 $362(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 $1.3 billion at June 30, 2016, and $888 million at December 31, 2015, which includes a fair value derivative adjustment of $971 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.

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- Definition Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258 + Details
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- Definition Fair value of financial instrument classified as a liability measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258 + Details
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