Financing Activities (LT Debt and Equity Securities) (Details) In Millions, except Share data, unless otherwise specified	1 Months Ended
	Apr. 30, 2012 USD ($) Integer	Apr. 30, 2012 UK [Member] Senior Unsecured Notes [Member] USD ($)	Apr. 30, 2012 UK [Member] Senior Unsecured Notes [Member] GBP (£)
Equity Securities (Numeric) [Abstract]
Stock issuance date	Apr. 01, 2012
Shares of common stock to be issued in a future period	9,900,000
Additional shares of common stock to be purchased by underwriters in a future period to cover over-allotments	590,880
Number of shares of common stock covered by a forward contract	9,900,000
Additional shares to cover over-allotments covered by a forward contract	590,880
Number of counterparties involved in the sale agreements	2
Settlement date of initial forward sale agreements	Apr. 30, 2013
Settlement date of subsequent forward sale agreements	Jul. 31, 2013
Initial forward price used to calculate the forward sale price	$ 27.02
Long-term Debt (Numeric) [Abstract]
Principal amount			£ 100
Stated interest rate		5.25%	5.25%
Maturity date (in year)		Dec. 31, 2023	Dec. 31, 2023
Net proceeds from issuance of unsecured debt		178	111
Number of shares of Preference Stock to be redeemed	2,500,000
Percentage rate on Preference Stock to be redeemed	6.25%
Redemption value of Preference Stock to be redeemed (in dollars per share)	$ 100
Date Preference Stock will be redeemed	Jun. 18, 2012
Payment for the par value of Preference Stock to be redeemed	$ 250