Shareholders' Equity Shareholders' Equity (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	1 Months Ended		1 Months Ended
	Oct. 31, 2013 Redeemable Preferred Stock [Member] Subsequent Event [Member] preferred_stock_series	Oct. 31, 2013 Nonredeemable Preferred Stock [Member] Subsequent Event [Member] preferred_stock_series	May 31, 2013 Serial Preferred Stock, 5.00 Percent Annual Dividend Rate [Member] Redeemable Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock, par or stated value per share			$ 100
Preferred stock, dividend rate, percentage			5.00%
Preferred stock, redemption price per share			$ 100
Preferred stock, number of series scheduled for redemption and cancellation	5
Preferred stock, total value of scheduled redemption and cancellation at stated redemption prices	$ 36
Preferred stock, date of scheduled redemption and cancellation	Nov. 30, 2013
Number of series of non-redeemable preferred stock outstanding following scheduled redemption		2
Aggregate stated value of remaining preferred stock following scheduled redemption		$ 2