Postretirement Benefits (Details 3) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Postretirement Benefits
Funded status at end of period	$ (201)	$ (140)
Pension liability recorded in the Consolidated Statement of Financial Position:
Pension liabilities - due within one year	(2)	(1)
Pension liabilities - due after one year	(199)	(139)
Net amount recognized	(201)	(140)
Employee pension plan
Postretirement Benefits
Expected employer contribution during next fiscal year	$ 17