Analysis of Cost or Amortized Cost, Gross Unrealized Gains and Losses and Fair Value for Investments (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]
Cost or amortized cost	$ 10,500	$ 10,246
Gross unrealized gains	1,673	1,542
Gross unrealized losses	9	53
Fair value	12,164	11,735
Debt Securities
Schedule of Available-for-sale Securities [Line Items]
Cost or amortized cost	8,252	8,084
Gross unrealized gains	780	713
Gross unrealized losses	7	18
Fair value	9,025	8,779
Debt Securities \| US States and Political Subdivisions Debt Securities
Schedule of Available-for-sale Securities [Line Items]
Cost or amortized cost	3,033	3,006
Gross unrealized gains	250	246
Fair value	3,283	3,252
Debt Securities \| Convertibles and Bonds with Warrants Attached
Schedule of Available-for-sale Securities [Line Items]
Cost or amortized cost	51	59
Fair value	51	59
Debt Securities \| US Government Agencies Debt Securities
Schedule of Available-for-sale Securities [Line Items]
Cost or amortized cost	7	6
Gross unrealized gains	1	1
Fair value	8	7
Debt Securities \| US Government-sponsored Enterprises Debt Securities
Schedule of Available-for-sale Securities [Line Items]
Cost or amortized cost	86	159
Gross unrealized gains		1
Fair value	86	160
Debt Securities \| Foreign Government
Schedule of Available-for-sale Securities [Line Items]
Cost or amortized cost	3	3
Fair value	3	3
Debt Securities \| Corporate Bond Securities
Schedule of Available-for-sale Securities [Line Items]
Cost or amortized cost	5,072	4,851
Gross unrealized gains	529	465
Gross unrealized losses	7	18
Fair value	5,594	5,298
Equity Securities
Schedule of Available-for-sale Securities [Line Items]
Cost or amortized cost	2,248	2,162
Gross unrealized gains	893	829
Gross unrealized losses	2	35
Fair value	3,139	2,956
Equity Securities \| Common Stock
Schedule of Available-for-sale Securities [Line Items]
Cost or amortized cost	2,149	2,088
Gross unrealized gains	860	801
Gross unrealized losses	2	35
Fair value	3,007	2,854
Equity Securities \| Preferred Stock
Schedule of Available-for-sale Securities [Line Items]
Cost or amortized cost	99	74
Gross unrealized gains	33	28
Fair value	$ 132	$ 102

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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-Publisher FASB

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Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 12

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Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

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Reference 4: http://www.xbrl.org/2003/role/presentationRef

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Reference 5: http://www.xbrl.org/2003/role/presentationRef

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-Number FAS115-1/124-1

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Reference 6: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

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-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 13

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Reference 9: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

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-Name Statement of Financial Accounting Standard (FAS)

-Number 133

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+ Details

- Definition

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.

+ References+ Details

- 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.

+ References+ Details