Analysis of Cost or Amortized Cost, Gross Unrealized Gains and Losses and Fair Value for Investments (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	$ 10,246	$ 10,174
Gross Unrealized Gains	1,542	1,299
Gross Unrealized Losses	53	49
Fair Value	11,735	11,424
Debt Securities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	8,084	7,888
Gross Unrealized Gains	713	515
Gross Unrealized Losses	18	20
Fair Value	8,779	8,383
Debt Securities \| US States and Political Subdivisions Debt Securities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	3,006	3,043
Gross Unrealized Gains	246	110
Gross Unrealized Losses		10
Fair Value	3,252	3,143
Debt Securities \| Convertibles and Bonds with Warrants Attached
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	59	69
Fair Value	59	69
Debt Securities \| US Government Agencies Debt Securities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	6	4
Gross Unrealized Gains	1	1
Fair Value	7	5
Debt Securities \| US Government-sponsored Enterprises Debt Securities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	159	201
Gross Unrealized Gains	1
Gross Unrealized Losses		1
Fair Value	160	200
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	4,851	4,568
Gross Unrealized Gains	465	404
Gross Unrealized Losses	18	9
Fair Value	5,298	4,963
Equity Securities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	2,162	2,286
Gross Unrealized Gains	829	784
Gross Unrealized Losses	35	29
Fair Value	2,956	3,041
Equity Securities \| Common Stock
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	2,088	2,211
Gross Unrealized Gains	801	757
Gross Unrealized Losses	35	28
Fair Value	2,854	2,940
Equity Securities \| Preferred Stock
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	74	75
Gross Unrealized Gains	28	27
Gross Unrealized Losses		1
Fair Value	$ 102	$ 101

For an unclassified balance sheet, this item represents investments in debt and equity securities which are categorized neither as held-to-maturity nor trading.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 45

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6871852&loc=d3e26610-111562

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 12

-Subparagraph b

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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

-Publisher FASB

-Name FASB Staff Position (FSP)

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-Paragraph 15E

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 133

-Paragraph 22

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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

-Publisher FASB

-Name FASB Staff Position (FSP)

-Number FAS115-1/124-1

-Paragraph 15D

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 13

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 7: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name FASB Staff Position (FSP)

-Number FAS115-1/124-1

-Paragraph 15C

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 8: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 14

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 16

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 10: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 25

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6379932&loc=d3e22054-111558

+ 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