Shareowners' Equity (Parenthetical) (Details) (USD $) In Millions, except Share data, unless otherwise specified				12 Months Ended
	Mar. 31, 2013	Dec. 31, 2012	Jun. 30, 2012 First Preferred Shares Issuance [Member]	Dec. 31, 2012 Second Preferred Shares Issuance [Member]	Sep. 30, 2012 Second Preferred Shares Issuance [Member]
Noncontrolling Interest [Line Items]
Preferred Stock, Shares Issued	40,000	40,000	22,500		17,500
Preferred Stock, Par or Stated Value Per Share	$ 0.01	$ 0.01
Proceeds From Issuance Of Preferred Stock				$ 3,960
Initial Fixed Interest Rate Of Preferred Stock			7.125%		6.25%
Percentage Points Over Three Month LIBOR			5.296%		4.704%