Significant Financing Transactions - (Narrative) (Details) (USD $) Share data in Millions, except Per Share data, unless otherwise specified	6 Months Ended				3 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011 Maximum [Member]	Jun. 30, 2011 Minimum [Member]	Mar. 31, 2011 Senior Notes 4.45 Percent Due 2021 [Member]	Mar. 31, 2011 Senior Notes 1.80 Percent Due 2014 [Member]	Dec. 31, 2010 Massachusetts Development Finance Agency Recovery Zone Facility Bonds, Series 2010 A [Member]	Dec. 31, 2010 Solid Waste Disposal Revenue Bonds, Series 2010 B [Member]
Borrowings							$ 160,000,000	$ 75
Issuance of long-term debt	1,060,000,000				500,000,000	400,000,000
Debt instrument, interest rate					4.45%	1.80%
Debt maturity					2021	2014
Contingent convertible senior notes	199,000,000
Conversion rate, shares of common stock per $1,000 principal amount of senior notes	28.7160
Conversion rate, shares of common stock per $1,000 principal amount of senior notes, conversion price	$ 34.82
Principal amount of senior notes	1,000
Common stock, shares issued	1
Common stock, cash proceeds	32,000,000	48,000,000
Repurchase of common stock	$ 601,000,000	$ 500,000,000	$ 700,000,000	$ 600,000,000
Repurchase of common stock, shares	13
Conversion share price unmet	$ 46.37
Minimum consecutive trading days	20
Maximum consecutive trading days	30