Debt And Shareholders' Equity (Schedule Of Changes In Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Debt And Shareholders' Equity [Line Items]
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Tax			$ 40	$ 34
Net Income (Loss) Available to Common Stockholders, Basic	$ 152	$ 117	436	286
Income Tax Expense (Benefit)	83	65	207	166
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax			67	69
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax			(2)	(5)
Beginning balance			(122)	(54)
Other comprehensive income (loss)	(8)	(14)	65	64
Ending balance	(57)	10	(57)	10
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Tax			0	6
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, Tax			0	1
Other Comprehensive Income (Loss), Tax			40	41
Accumulated Net Unrealized Investment Gain (Loss) [Member]
Debt And Shareholders' Equity [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax			65	54
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax			0	0
Beginning balance			(93)	(18)
Other comprehensive income (loss)			65	54
Ending balance	(28)	36	(28)	36
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Debt And Shareholders' Equity [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax			2	16
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax			(2)	(5)
Beginning balance			2	2
Other comprehensive income (loss)			0	11
Ending balance	2	13	2	13
Accumulated Defined Benefit Plans Adjustment [Member]
Debt And Shareholders' Equity [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax			0	(1)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax			0	0
Beginning balance			(31)	(38)
Other comprehensive income (loss)			0	(1)
Ending balance	(31)	(39)	(31)	(39)
Interest Rate Contract [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Debt And Shareholders' Equity [Line Items]
Gain (Loss) on Derivative Instruments, Net, Pretax	0	3	3	9
Net Income (Loss) Available to Common Stockholders, Basic	0	2	2	5
Income Tax Expense (Benefit)	$ 0	$ 1	$ 1	$ 4