Common Shareholders' Equity (Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ (70)	$ (167)
Other comprehensive income (loss) before reclassifications	48	18
Amounts reclassified from AOCI	(7)	22
Total other comprehensive income, net of tax	41	40	[1]
Less other comprehensive loss attributable to noncontrolling interests	11	(14)
Ending balance	(40)	(113)
Net Unrealized Gains (Losses) on Cash Flow Hedges
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(100)	(170)
Other comprehensive income (loss) before reclassifications	0	0
Amounts reclassified from AOCI	9	23
Total other comprehensive income, net of tax	9	23
Less other comprehensive loss attributable to noncontrolling interests	10	(1)
Ending balance	(101)	(146)
Net Unrealized Gains (Losses) on Available for Sale Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	225	174
Other comprehensive income (loss) before reclassifications	34	8
Amounts reclassified from AOCI	(16)	(1)
Total other comprehensive income, net of tax	18	7
Less other comprehensive loss attributable to noncontrolling interests	0	0
Ending balance	243	181
Defined Benefit Pension and Other Benefits Plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(83)	(62)
Other comprehensive income (loss) before reclassifications	(3)	(7)
Amounts reclassified from AOCI	0	0
Total other comprehensive income, net of tax	(3)	(7)
Less other comprehensive loss attributable to noncontrolling interests	0	0
Ending balance	(86)	(69)
Net Unrealized Gains (Losses) on Foreign Currency Translation
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(90)	(85)
Other comprehensive income (loss) before reclassifications	16	20
Amounts reclassified from AOCI	0	0
Total other comprehensive income, net of tax	16	20
Less other comprehensive loss attributable to noncontrolling interests	1	(13)
Ending balance	(75)	(52)
Other Comprehensive Income (Loss) Related to Equity Method Investee
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(22)	(24)
Other comprehensive income (loss) before reclassifications	1	(3)
Amounts reclassified from AOCI	0	0
Total other comprehensive income, net of tax	1	(3)
Less other comprehensive loss attributable to noncontrolling interests	0	0
Ending balance	$ (21)	$ (27)

[1] Amounts have been retrospectively adjusted. See Note 7 - Stock-Based Compensation.