Employee Benefit Plans (Accumulated Benefit Obligation in Excess of Plan Assets) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012		Dec. 31, 2011
General Discussion of Pension and Other Postretirement Benefits [Abstract]
Accumulated benefit obligation	$ 4,850	[1]	$ 95
Fair value of plan assets	$ 4,189	[1]	$ 0

[1] The increase from 2011 is primarily due to a decrease in the discount rate.