Debt (Revolving Credit Facility And Commercial Paper) (Details) (USD $)	12 Months Ended
	Dec. 31, 2012
Outstanding commercial paper obligations	$ 0
$800 Million Credit Facility [Member]
Amount available for borrowing	800,000,000
Amount available for borrowing	1,250,000,000
Maximum amount of letters of credit issuable under the facility	100,000,000
Revolving credit facility expiration date	Dec. 01, 2017
Line of Credit Facility, Competitive Bid Loans, Max	$ 500,000,000
Original Expiration Date [Member] | $800 Million Credit Facility [Member]
Revolving credit facility expiration date	Dec. 02, 2016