Fair Value Measurements Narrative (Details) (Investment Segment [Member], USD $) In Millions, unless otherwise specified	6 Months Ended
Jun. 30, 2013
Fair Value, Instruments Classified in Shareholders' Equity Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Change in fair value of loan from 1 percent change in risk premium	2.00%
Level 3 [Member]
Fair Value, Instruments Classified in Shareholders' Equity Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Unrealized losses included in earnings related to Level 3 investments	$ 4

Amount of unrealized (holding) gain (loss) which is included in the statement of income (or changes in net assets) related to those assets still held at the reporting date for which fair value is measured on a recurring basis using significant unobservable inputs (Level 3).

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (d)

-URI http://asc.fasb.org/extlink&oid=25499696&loc=d3e19207-110258

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration