Employee Benefits (Details 4) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012
Retirement Plans [Member]
Information about the expected cash flows for retirement and post-retirement plans and impact of the Medicare subsidy
2013, Net payments	$ 72	[1]
2014, Net payments	75	[1]
2015, Net payments	78	[1]
2016, Net payments	82	[1]
2017, Net payments	86	[1]
2018-2022, Net payments	484	[1]
Postretirement Plans [Member]
Information about the expected cash flows for retirement and post-retirement plans and impact of the Medicare subsidy
2013, Gross payments	19	[2]
2014, Gross payments	21	[2]
2015, Gross payments	22	[2]
2016, Gross payments	24	[2]
2017, Gross payments	25	[2]
2018-2022, Gross payments	151	[2]
2013, Retiree Contributions	(7)	[2]
2014, Retiree Contributions	(8)	[2]
2015, Retiree Contributions	(10)	[2]
2016, Retiree Contributions	(12)	[2]
2017, Retiree Contributions	(14)	[2]
2018-2022, Retiree Contributions	(98)	[2]
2013, Medicare subsidy	(1)	[2]
2014, Medicare subsidy	(1)	[2]
2015, Medicare subsidy	(1)	[2]
2016, Medicare subsidy	(1)	[2]
2017, Medicare subsidy	(1)	[2]
2018-2022, Medicare subsidy	(3)	[2]
2013, Net payments	11	[2]
2014, Net payments	12	[2]
2015, Net payments	11	[2]
2016, Net payments	11	[2]
2017, Net payments	10	[2]
2018-2022, Net payments	$ 50	[2]

[1] Reflects the total benefits expected to be paid from the plans or from our assets including both our share of the benefit cost and the participants’ share of the cost.

[2] Reflects the total benefits expected to be paid from our assets.