Shareholders' Equity (Details) (USD $) In Millions, except Share data in Thousands, unless otherwise specified	1 Months Ended	3 Months Ended			9 Months Ended		12 Months Ended
	Jan. 31, 2012	Sep. 30, 2012	Mar. 31, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2012
Equity [Abstract]
Percentage increase in cash dividend	11.10%
Dividends per share (usd per share)		$ 0.1	$ 0.10	$ 0.09	$ 0.3	$ 0.27	$ 0.40
Dividends paid		$ 56		$ 48	$ 167	$ 145
Stock repurchased during period (shares)					28
Weighted average repurchase price (usd per share)		$ 35.18			$ 35.18