Investment Securities (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Schedule of Available for Sale Securities by Type
Cost	$ 5,145	$ 6,806
Gross Unrealized Gains	474	416
Gross Unrealized Losses	(5)	(75)
Estimated Fair Value	5,614	7,147
U.S. States and Political Subdivisions Debt Securities [Member]
Schedule of Available for Sale Securities by Type
Cost	4,280	4,968
Gross Unrealized Gains	199	103
Gross Unrealized Losses	(5)	(72)
Estimated Fair Value	4,474	4,999
U.S. Government agency obligations [Member]
Schedule of Available for Sale Securities by Type
Cost	3	352
Gross Unrealized Gains	0	2
Gross Unrealized Losses	0	0
Estimated Fair Value	3	354
U.S. Government treasury obligations [Member]
Schedule of Available for Sale Securities by Type
Cost	330	330
Gross Unrealized Gains	8	10
Gross Unrealized Losses	0	0
Estimated Fair Value	338	340
Corporate debt securities [Member]
Schedule of Available for Sale Securities by Type
Cost	73	626
Gross Unrealized Gains	6	9
Gross Unrealized Losses	0	(3)
Estimated Fair Value	79	632
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Schedule of Available for Sale Securities by Type
Cost	210	261
Gross Unrealized Gains	14	17
Gross Unrealized Losses	0	0
Estimated Fair Value	224	278
Equity securities [Member]
Schedule of Available for Sale Securities by Type
Cost	64	95
Gross Unrealized Gains	232	265
Gross Unrealized Losses	0	0
Estimated Fair Value	296	360
Foreign government bonds and obligations [Member]
Schedule of Available for Sale Securities by Type
Cost	134	120
Gross Unrealized Gains	15	10
Gross Unrealized Losses	0	0
Estimated Fair Value	149	130
Availabe For Sale Securities Other [Member]
Schedule of Available for Sale Securities by Type
Cost	51	54
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	$ 51	$ 54

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

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

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

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

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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.

+ 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