Common Shareholders' Equity (Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Accumulated other comprehensive loss, beginning	$ (167)	$ (40)	$ 56
Other comprehensive income (loss) before reclassifications	45	(164)	(156)
Amounts reclassified from AOCI	52	26	58
Total other comprehensive income (loss), net of tax	97	(138)	(98)
Less other comprehensive income attributable to noncontrolling interests	0	(11)	(2)
Accumulated other comprehensive loss, ending	(70)	(167)	(40)
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Accumulated other comprehensive loss, beginning	(170)	(156)	(115)
Other comprehensive income (loss) before reclassifications	0	(88)	(141)
Amounts reclassified from AOCI	70	63	98
Total other comprehensive income (loss), net of tax	70	(25)	(43)
Less other comprehensive income attributable to noncontrolling interests	0	(11)	(2)
Accumulated other comprehensive loss, ending	(100)	(170)	(156)
Accumulated Net Unrealized Investment Gain (Loss) [Member]
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Accumulated other comprehensive loss, beginning	174	218	197
Other comprehensive income (loss) before reclassifications	69	(7)	62
Amounts reclassified from AOCI	(18)	(37)	(41)
Total other comprehensive income (loss), net of tax	51	(44)	21
Less other comprehensive income attributable to noncontrolling interests	0	0	0
Accumulated other comprehensive loss, ending	225	174	218
Accumulated Defined Benefit Plans Adjustment [Member]
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Accumulated other comprehensive loss, beginning	(62)	(20)	23
Other comprehensive income (loss) before reclassifications	(21)	(42)	(44)
Amounts reclassified from AOCI	0	0	1
Total other comprehensive income (loss), net of tax	(21)	(42)	(43)
Less other comprehensive income attributable to noncontrolling interests	0	0	0
Accumulated other comprehensive loss, ending	(83)	(62)	(20)
Accumulated Translation Adjustment [Member]
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Accumulated other comprehensive loss, beginning	(85)	(58)	(33)
Other comprehensive income (loss) before reclassifications	(5)	(27)	(25)
Amounts reclassified from AOCI	0	0	0
Total other comprehensive income (loss), net of tax	(5)	(27)	(25)
Less other comprehensive income attributable to noncontrolling interests	0	0	0
Accumulated other comprehensive loss, ending	(90)	(85)	(58)
Accumulated Income (Loss) Related to Equity Method Investee [Member]
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Accumulated other comprehensive loss, beginning	(24)	(24)	(16)
Other comprehensive income (loss) before reclassifications	2	0	(8)
Amounts reclassified from AOCI	0	0	0
Total other comprehensive income (loss), net of tax	2	0	(8)
Less other comprehensive income attributable to noncontrolling interests	0	0	0
Accumulated other comprehensive loss, ending	$ (22)	$ (24)	$ (24)