Debt And Shareholders' Equity (Schedule Of Changes In Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Debt And Shareholders' Equity [Line Items]
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Tax	$ (41)	$ 7
Net Income (Loss) Available to Common Stockholders, Basic	231	129
Income Tax Expense (Benefit)	70	45
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	(128)	12
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	0	(1)
Beginning balance	(139)	(122)
Other comprehensive income (loss)	(128)	11
Ending balance	(267)	(111)
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Tax	(1)	(1)
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, Tax	0	0
Other Comprehensive Income (Loss), Tax	(42)	6
Accumulated Net Unrealized Investment Gain (Loss) [Member]
Debt And Shareholders' Equity [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	(126)	12
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	0	0
Beginning balance	(114)	(93)
Other comprehensive income (loss)	(126)	12
Ending balance	(240)	(81)
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)	0
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	0	(1)
Beginning balance	(2)	2
Other comprehensive income (loss)	(2)	(1)
Ending balance	(4)	1
Accumulated Defined Benefit Plans Adjustment [Member]
Debt And Shareholders' Equity [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	0	0
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	0	0
Beginning balance	(23)	(31)
Other comprehensive income (loss)	0	0
Ending balance	(23)	(31)
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	2
Reclassification from AOCI, Current Period, Tax	0	1
Income Tax Expense (Benefit)	$ 0	$ 1