Investments in Securities Other-than-temporary Impairments 1 (Details) (USD $) In Billions, unless otherwise specified	Mar. 31, 2013
Investments, Debt and Equity Securities [Abstract]
Gross unrealized losses on available-for-sale securities that had existed for a period of 12 consecutive months or longer	$ 1.3
Fair value of securities with unrealized losses for 12 consecutive months or longer as percentage of amortized cost basis	89.00%

Amount of the excess of amortized cost basis over fair value of securities in a loss position and categorized neither as held-to-maturity nor trading securities.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 6

-Subparagraph (a)(2)

-URI http://asc.fasb.org/extlink&oid=6872113&loc=d3e27290-111563

Name:	us-gaap_AvailableforsaleSecuritiesContinuousUnrealizedLossPositionAggregateLosses2
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant