Employee Benefit Plans (Quarterly Info) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Pension Benefits [Member]
Components of net periodic benefit cost:
Service cost	$ 10	$ 11
Interest cost	16	13
Expected return on plan assets	(19)	(15)
Amortization of net actuarial loss	9	15
Net periodic benefit cost	16	24
Employer contributions	16
Estimated future employer contributions in current fiscal year	47
Other Postretirement Benefits [Member]
Components of net periodic benefit cost:
Service cost	1	1
Interest cost	2	3
Expected return on plan assets	(3)	(2)
Amortization of prior service cost (credit)	(5)	(2)
Amortization of net actuarial loss	0	2
Reclassification to regulatory liability	1	0
Net periodic benefit cost	(4)	2
Amortization of prior service cost (credit) from regulatory assets (liabilities)	(3)	(1)
Amortization of net actuarial loss (gain) from regulatory assets (liabilities)	0	1
Employer contributions	2
Estimated future employer contributions in current fiscal year	$ 6