Borrowings (Narrative) (Details) (USD $) In Millions	6 Months Ended
Jun. 30, 2011	Dec. 31, 2010
Senior Notes - 2007 [Member]
Estimated fair value of senior notes	$ 587	$ 585
Senior Notes - 2006 [Member]
Estimated fair value of senior notes	353	357
Repayments of debt	$ 100

Estimated fair value of the debt instrument at the balance-sheet date.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 107
-Paragraph 10

Name:	us-gaap_DebtInstrumentFairValue
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant