Pension and Other Postretirement Benefits (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended							12 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2013 Pension Benefits [Member]	Mar. 31, 2012 Pension Benefits [Member]	Mar. 31, 2013 Other Postretirement Benefits [Member]	Mar. 31, 2012 Other Postretirement Benefits [Member]	Mar. 31, 2013 Retiree Health Benefits [Member]	Dec. 31, 2012 Retiree Life Insurance Benefits [Member]	Dec. 31, 2012 Retiree Life Insurance Benefits [Member] Scenario, Previously Reported [Member]
Change in benefit obligation [Abstract]
Service cost			$ 1	$ 1	$ 0	$ 0
Interest cost			45	49	3	4
Amendments							(57)
Components of net pension cost and other postretirement benefits cost tables detail [Abstract]
Service cost			1	1	0	0
Interest cost			45	49	3	4
Expected long-term return on plan assets			(68)	(67)	0	0
Amortization of net loss from past experience			19	15	0	0
Amortization of prior service cost			0	0	(2)	(3)
Curtailment gain			0	0	(19)	0
Settlement loss			0	6	0	0
Net pension cost			(3)	4	(18)	1
Pension And Other Postretirement Footnote Text Details [Abstract]
Increase (decrease) to postretirement benefits liability adjustment pre-tax	(61)	(18)
Increase (decrease) to postretirement benefits liability adjustement after-tax	(40)	(11)
Weighted average amortization period for amortization of past experience								2 years 6 months
Expected pre-tax gains (losses) related to amortization of net prior service cost								4	9
Average life expectancy of frozen plan participants							25 years
Domestic qualified pension plan contributions	6
Expected plan contributions during remainder of current fiscal year	$ 244