Employee Benefits Schedule of Changes in Fair Value of Plan Assets (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	$ 537	$ 487
Private Equity Funds [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	32	32	23	17
Purchases and sales, net			4
Purchases	(1)	7
Realized gain on sales			1
Realized loss on sales	(1)	(2)
Unrealized gain on assets	2	4	1
alternative assets [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	0	30	28	23
Purchases and sales, net			2
Purchases	(30)	0
Realized gain on sales			0
Realized loss on sales	6	0
Unrealized gain on assets	(6)	2	3
Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	32	62	51	40
Purchases and sales, net			6
Purchases	(31)	7
Realized gain on sales			1
Realized loss on sales	5	(2)
Unrealized gain on assets	$ (4)	$ 6	$ 4