Debt (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012 Financial_Covenants	Mar. 31, 2012 5.875% Notes and Debentures due July 2012 [Member]	Mar. 31, 2012 5.95% Notes and Debentures due March 15, 2022 [Member]	Mar. 05, 2012 5.95% Notes and Debentures due March 15, 2022 [Member]
Debt Instrument [Line Items]
Interest on notes		5.875%	5.95%
Issued notes	$ 400	$ 745		$ 400
Debt (Textual) [Abstract]
Additional borrowing capacity	783
Effective interest for notes	6.50%
Absorption of reduction to shareholders' equity to remain in compliance with covenant	422
Financial covenants	2
Company repurchased Notes in open-market transactions	46
Premium paid on repurchase of notes	1
Borrowings under Five Year Revolving Credit Agreement	$ 0