Employee Benefit Plans (Schedule of Changes, Net of Tax, in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income (Loss) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Actuarial loss arising during the period	$ (240)	$ 286	$ (192)
Amortization of actuarial net loss	39	89	62
Amortization of prior service cost	3	2	3
Total recognized in other comprehensive income (loss)	(198)	377	(123)
Qualified Plan
Actuarial loss arising during the period	(196)
Amortization of actuarial net loss	31
Amortization of prior service cost	6
Total recognized in other comprehensive income (loss)	(159)
Non-Qualified Plan
Actuarial loss arising during the period	(38)
Amortization of actuarial net loss	7
Amortization of prior service cost	(4)
Total recognized in other comprehensive income (loss)	(35)
Postretirement Benefit Plan
Actuarial loss arising during the period	(6)
Amortization of actuarial net loss	1
Amortization of prior service cost	1
Total recognized in other comprehensive income (loss)	$ (4)