Debt and Banking Arrangements (Details) (USD $) In Millions	Jun. 30, 2011
Letters of credit issued and loans outstanding under line of credit facilities
Letters of Credit Outstanding, Amount	$ 74
Loans outstanding	350
$ 900 million unsecured credit facility
Letters of credit issued and loans outstanding under line of credit facilities
Letters of Credit Outstanding, Amount	0
Loans outstanding	0
$ 2 billion WPZ unsecured credit facility
Letters of credit issued and loans outstanding under line of credit facilities
Letters of Credit Outstanding, Amount	0
Loans outstanding	350
Bilateral bank agreements for letters of credit
Letters of credit issued and loans outstanding under line of credit facilities
Letters of Credit Outstanding, Amount	74
Loans outstanding	$ 0