Investments (Amortized Cost and Fair Values of Securities) (Detail) (USD $) In Millions, unless otherwise specified	9 Months Ended	12 Months Ended
Sep. 30, 2012	Dec. 31, 2011
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or Amortized Cost	$ 39,067	$ 38,368
Gross Unrealized Gains	4,672	3,225
Gross Unrealized Losses	291	626
Estimated Fair Value	43,448	40,967
Unrealized OTTI Losses (Gains)	(15)	97
Fixed Maturity Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or Amortized Cost	38,093	37,466
Gross Unrealized Gains	4,546	3,128
Gross Unrealized Losses	210	554
Estimated Fair Value	42,429	40,040
Unrealized OTTI Losses (Gains)	(15)	97
Corporate And Other Bonds [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or Amortized Cost	19,209	19,086
Gross Unrealized Gains	2,634	1,946
Gross Unrealized Losses	32	154
Estimated Fair Value	21,811	20,878
States, Municipalities And Political Subdivisions [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or Amortized Cost	9,415	9,018
Gross Unrealized Gains	1,450	900
Gross Unrealized Losses	53	136
Estimated Fair Value	10,812	9,782
Residential Mortgage-Backed Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or Amortized Cost	5,907	5,786
Gross Unrealized Gains	264	172
Gross Unrealized Losses	81	183
Estimated Fair Value	6,090	5,775
Unrealized OTTI Losses (Gains)	(12)	99
Commercial Mortgage-Backed Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or Amortized Cost	1,582	1,365
Gross Unrealized Gains	123	48
Gross Unrealized Losses	17	59
Estimated Fair Value	1,688	1,354
Unrealized OTTI Losses (Gains)	(3)	(2)
Other Asset-Backed [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or Amortized Cost	944	946
Gross Unrealized Gains	23	13
Gross Unrealized Losses	1	4
Estimated Fair Value	966	955
Asset-Backed Securities [Member] \| Fixed Maturity Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or Amortized Cost	8,433	8,097
Gross Unrealized Gains	410	233
Gross Unrealized Losses	99	246
Estimated Fair Value	8,744	8,084
Unrealized OTTI Losses (Gains)	(15)	97
U.S. Treasury And Obligations Of Government-Sponsored Enterprises [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or Amortized Cost	182	479
Gross Unrealized Gains	11	14
Gross Unrealized Losses	1
Estimated Fair Value	192	493
Foreign Government [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or Amortized Cost	588	608
Gross Unrealized Gains	26	28
Estimated Fair Value	614	636
Redeemable Preferred Stock [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or Amortized Cost	101	51
Gross Unrealized Gains	14	7
Estimated Fair Value	115	58
Fixed Maturities Available-For-Sale [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or Amortized Cost	37,928	37,339
Gross Unrealized Gains	4,545	3,128
Gross Unrealized Losses	185	536
Estimated Fair Value	42,288	39,931
Unrealized OTTI Losses (Gains)	(15)	97
Fixed Maturities, Trading [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or Amortized Cost	165	127
Gross Unrealized Gains	1
Gross Unrealized Losses	25	18
Estimated Fair Value	141	109
Common Stock [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or Amortized Cost	22	30
Gross Unrealized Gains	24	17
Estimated Fair Value	46	47
Preferred Stock [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or Amortized Cost	206	258
Gross Unrealized Gains	8	4
Gross Unrealized Losses		5
Estimated Fair Value	214	257
Equity Securities Available-For-Sale [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or Amortized Cost	228	288
Gross Unrealized Gains	32	21
Gross Unrealized Losses		5
Estimated Fair Value	260	304
Equity Securities, Trading [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or Amortized Cost	746	614
Gross Unrealized Gains	94	76
Gross Unrealized Losses	81	67
Estimated Fair Value	759	623
Equity Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or Amortized Cost	974	902
Gross Unrealized Gains	126	97
Gross Unrealized Losses	81	72
Estimated Fair Value	$ 1,019	$ 927

This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

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This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents Available-for-sale Securities which consist of all investments in certain debt and equity securities neither classified as trading or held-to-maturity securities. A debt security represents a creditor relationship with an enterprise. Debt securities include, among other items, US Treasury securities, US government securities, municipal securities, corporate bonds, convertible debt, commercial paper, and all securitized debt instruments. An equity security represents an ownership interest in an enterprise or the right to acquire or dispose of an ownership interest in an enterprise at fixed or determinable prices. Equity securities include, among other things, common stock, certain preferred stock, warrant rights, call options, and put options, but do not include convertible debt. An entity may opt to provide the reader with additional narrative text to better understand the nature of investments in debt and equity securities which are categorized as Available-for-sale.

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- Definition

This item represents the gross unrealized gains for securities, at a point in time, which are categorized neither as held-to-maturity nor trading securities.

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