Debt and Banking Arrangements (Details) (USD $) In Millions	Sep. 30, 2011
Letters of credit issued and loans outstanding under line of credit facilities
Letters of Credit Outstanding, Amount	$ 89
Loans outstanding	400
$ 900 million unsecured credit facility
Letters of credit issued and loans outstanding under line of credit facilities
Letters of Credit Outstanding, Amount	0	[1]
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	[2]
Loans outstanding	400
Bilateral bank agreements for letters of credit
Letters of credit issued and loans outstanding under line of credit facilities
Letters of Credit Outstanding, Amount	$ 89

[1] $700 million letter of credit capacity.

[2] $1.3 billion letter of credit capacity.