Common Shareholders' Equity (Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Components Of Comprehensive Income And Accumulated Other Comprehensive Income Loss [Line Items]
Beginning balance	$ (73)	$ 21	$ (40)	$ 56
Other comprehensive income (loss) before reclassifications	51	47	8	27
Amounts reclassified from AOCI	19	(9)	26	(24)
Net other comprehensive income (loss)	70	38	34	3
Less other comprehensive income attributable to noncontrolling interests	(1)		2
Ending balance	(4)	59	(4)	59
Net Unrealized Gains (Losses) on Cash Flow Hedges
Components Of Comprehensive Income And Accumulated Other Comprehensive Income Loss [Line Items]
Beginning balance	(189)	(124)	(156)	(115)
Other comprehensive income (loss) before reclassifications	40	(7)	(11)	(25)
Amounts reclassified from AOCI	22	(4)	39	5
Net other comprehensive income (loss)	62	(11)	28	(20)
Less other comprehensive income attributable to noncontrolling interests	(1)		0
Ending balance	(128)	(135)	(128)	(135)
Net Unrealized Gains (Losses) on Available for Sale Securities
Components Of Comprehensive Income And Accumulated Other Comprehensive Income Loss [Line Items]
Beginning balance	220	185	218	197
Other comprehensive income (loss) before reclassifications	(7)	40	5	53
Amounts reclassified from AOCI	(3)	(5)	(13)	(30)
Net other comprehensive income (loss)	(10)	35	(8)	23
Less other comprehensive income attributable to noncontrolling interests	0		0
Ending balance	210	220	210	220
Defined Benefit Pension and Other Benefits Plans
Components Of Comprehensive Income And Accumulated Other Comprehensive Income Loss [Line Items]
Beginning balance	(36)	28	(20)	23
Other comprehensive income (loss) before reclassifications	0	0	(16)	4
Amounts reclassified from AOCI	0	0	0	1
Net other comprehensive income (loss)	0	0	(16)	5
Less other comprehensive income attributable to noncontrolling interests	0		0
Ending balance	(36)	28	(36)	28
Net Unrealized Gains (Losses) on Foreign Currency Translation
Components Of Comprehensive Income And Accumulated Other Comprehensive Income Loss [Line Items]
Beginning balance	(42)	(50)	(58)	(33)
Other comprehensive income (loss) before reclassifications	15	17	29	0
Amounts reclassified from AOCI	0	0	0	0
Net other comprehensive income (loss)	15	17	29	0
Less other comprehensive income attributable to noncontrolling interests	0		2
Ending balance	(27)	(33)	(27)	(33)
Other Comprehensive Loss Related to Equity Method Investee
Components Of Comprehensive Income And Accumulated Other Comprehensive Income Loss [Line Items]
Beginning balance	(26)	(18)	(24)	(16)
Other comprehensive income (loss) before reclassifications	3	(3)	1	(5)
Amounts reclassified from AOCI	0	0	0	0
Net other comprehensive income (loss)	3	(3)	1	(5)
Less other comprehensive income attributable to noncontrolling interests	0		0
Ending balance	$ (23)	$ (21)	$ (23)	$ (21)