Financial Instruments (Narrative) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Dec. 31, 2010	Dec. 31, 2011
Financial Instruments [Abstract]
Additional long-term investments, no market prices	$ 42			$ 37
Gross unrealized gains on fiduciary assets during period	0		1
Gross unrealized losses (pre-tax) on fiduciary assets during period	$ 0	$ 3