Employee Benefit Plans Employee Benefit Plans - Unrecognized Amounts (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Reconciliation of Amounts Not Yet Recognized As Components of Net Periodic Benefit Cost [Roll Forward]
Amortization of net loss	$ 52
Amoritization of prior service credit	(15)
Amortization of regulatory deferrals	0
Amounts that will be amortized in next fiscal year	37
Pension [Member]
Defined Benefit Plan Disclosure [Line Items]
Net loss	520	361
Prior service credit	(21)	(29)
Regulatory deferrals	(3)	(4)
Total net periodic benefit cost not yet recognized	496	328	618
Reconciliation of Amounts Not Yet Recognized As Components of Net Periodic Benefit Cost [Roll Forward]
Net (gain) loss arising during the year	197	(242)
Net amortization	(29)	(48)
Total Net Periodic Benefit Cost Not Yet Recognized, Arising During Period	168	(290)
Amortization of net loss	50
Amoritization of prior service credit	(8)
Amortization of regulatory deferrals	(1)
Amounts that will be amortized in next fiscal year	41
Other Postretirement [Member]
Defined Benefit Plan Disclosure [Line Items]
Net loss	41	108
Prior service credit	(26)	(33)
Regulatory deferrals	2	2
Total net periodic benefit cost not yet recognized	17	77
Reconciliation of Amounts Not Yet Recognized As Components of Net Periodic Benefit Cost [Roll Forward]
Amortization of net loss	2
Amoritization of prior service credit	(7)
Amortization of regulatory deferrals	1
Amounts that will be amortized in next fiscal year	(4)
Regulatory Asset [Member] | Pension [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net periodic benefit cost not yet recognized	474	313	599
Reconciliation of Amounts Not Yet Recognized As Components of Net Periodic Benefit Cost [Roll Forward]
Net (gain) loss arising during the year	189	(239)
Net amortization	(28)	(47)
Total Net Periodic Benefit Cost Not Yet Recognized, Arising During Period	161	(286)
Regulatory Asset [Member] | Other Postretirement [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net periodic benefit cost not yet recognized	17	77	177
Reconciliation of Amounts Not Yet Recognized As Components of Net Periodic Benefit Cost [Roll Forward]
Net (gain) loss arising during the year	(58)	(92)
Net amortization	(2)	(8)
Total Net Periodic Benefit Cost Not Yet Recognized, Arising During Period	(60)	(100)
Accumulated Other Comprehensive Loss [Member] | Pension [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net periodic benefit cost not yet recognized	22	15	19
Reconciliation of Amounts Not Yet Recognized As Components of Net Periodic Benefit Cost [Roll Forward]
Net (gain) loss arising during the year	8	(3)
Net amortization	(1)	(1)
Total Net Periodic Benefit Cost Not Yet Recognized, Arising During Period	$ 7	$ (4)