Short-term Borrowings and Long-term Debt (Details) (Line of Credit [Member], USD $) In Millions, unless otherwise specified	12 Months Ended		9 Months Ended		9 Months Ended
	Dec. 31, 2011	Dec. 31, 2011 Unsecured International Revolving Credit Facility [Member]	Sep. 08, 2012 Unsecured Revolving Credit Facility [Member] Banks	Dec. 31, 2011 Unsecured Revolving Credit Facility [Member]	Sep. 08, 2012 Unsecured Revolving Credit Facility [Member] LIBOR [Member]
Debt Instrument [Line Items]
Line of credit facility, maximum commitment from participating banks		$ 350	$ 1,300	$ 1,150
Line of credit facility, expiration date	Nov. 22, 2012
Line of credit facility, number of participating banks			24
Line of credit facility, minimum commitment from participating banks			23
Line Of Credit Facility Maximum Commitment From Participating Banks			115
Unused credit facility			1,200
Outstanding letters of credit			88
Credit facility, outstanding borrowings			10
Debt instrument, lower range of basis spread on variable rate					1.00%
Debt instrument, upper range of basis spread on variable rate					1.75%
Debt instrument, description of variable rate basis					LIBOR
Minimum principal payment failure amount that constitutes default			$ 125