Common Shareholders' Equity (Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Components Of Comprehensive Income And Accumulated Other Comprehensive Income Loss [Line Items]
Beginning balance	$ (4)	$ 59	$ (40)	$ 56
Other comprehensive loss before reclassifications	(171)	(51)	(163)	(31)
Amounts reclassified from AOCI	3	39	29	22
Net other comprehensive loss	(168)	(12)	(134)	(9)
Less other comprehensive loss attributable to noncontrolling interests	4		6
Ending balance	(168)	47	(168)	47
Net Unrealized Gains (Losses) on Cash Flow Hedges
Components Of Comprehensive Income And Accumulated Other Comprehensive Income Loss [Line Items]
Beginning balance	(128)	(135)	(156)	(115)
Other comprehensive loss before reclassifications	(97)	(33)	(107)	(64)
Amounts reclassified from AOCI	11	45	50	56
Net other comprehensive loss	(86)	12	(57)	(8)
Less other comprehensive loss attributable to noncontrolling interests	2		1
Ending balance	(212)	(123)	(212)	(123)
Net Unrealized Gains (Losses) on Available for Sale Securities
Components Of Comprehensive Income And Accumulated Other Comprehensive Income Loss [Line Items]
Beginning balance	210	220	218	197
Other comprehensive loss before reclassifications	(38)	(12)	(33)	40
Amounts reclassified from AOCI	(8)	(6)	(21)	(35)
Net other comprehensive loss	(46)	(18)	(54)	5
Less other comprehensive loss attributable to noncontrolling interests	0		0
Ending balance	164	202	164	202
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 loss before reclassifications	0	0	(16)	4
Amounts reclassified from AOCI	0	0	0	1
Net other comprehensive loss	0	0	(16)	5
Less other comprehensive loss 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	(27)	(33)	(58)	(33)
Other comprehensive loss before reclassifications	(33)	(6)	(5)	(6)
Amounts reclassified from AOCI	0	0	0	0
Net other comprehensive loss	(33)	(6)	(5)	(6)
Less other comprehensive loss attributable to noncontrolling interests	2		5
Ending balance	(58)	(39)	(58)	(39)
Other Comprehensive Income (Loss) Related to Equity Method Investee
Components Of Comprehensive Income And Accumulated Other Comprehensive Income Loss [Line Items]
Beginning balance	(23)	(21)	(24)	(16)
Other comprehensive loss before reclassifications	(3)	0	(2)	(5)
Amounts reclassified from AOCI	0	0	0	0
Net other comprehensive loss	(3)	0	(2)	(5)
Less other comprehensive loss attributable to noncontrolling interests	0		0
Ending balance	$ (26)	$ (21)	$ (26)	$ (21)