Short-Term Borrowings (U.S. Government Securities And Related Repurchase Agreements Including Accrued Interest) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011
U.S. Government Securities Sold [Member]
Short-term Debt [Line Items]
Overnight maturity, Amortized Cost	$ 2,931
Overnight maturity, Fair Value	2,978
Repurchase Agreements [Member]
Short-term Debt [Line Items]
Overnight maturity, Amortized Cost	$ 2,921
Overnight maturity, Rate	0.001%

The interest rate associated with the repurchase agreements. This is also known as the repo rate.

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Article 4

-Section 08

-Paragraph m

-Subparagraph 1

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 235

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.4-08.(m)(1)(i)(A)(ii))

-URI http://asc.fasb.org/extlink&oid=6881521&loc=d3e23780-122690

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant