Accumulated Other Comprehensive Loss (Reconciliation Of The Components Of Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	$ 170	$ 941
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	289	80
Investments, net pretax unrealized (losses) gains excluding non-credit component of other-than-temporary impairments	(119)	861
Deferred tax asset (liability)	24	(310)
Net unrealized (losses) gains on investments excluding non-credit component of other-than-temporary impairments	(95)	551
Non-credit component of other than temporary impairments on investments, unrealized losses	(2)	0
Non-credit component of other than temporary impairments on investments, deferred tax asset	0	0
Net unrealized non-credit component of other than temporary impairments on investments	(2)	0
Cash flow hedges, gross unrealized losses	(315)	(363)
Cash flow hedges, deferred tax asset	66	127
Net unrealized losses on cash flow hedges	(249)	(236)
Defined benefit pension plans, deferred net actuarial loss	(587)	(633)
Defined benefit pension plans, deferred prior service credits	(1)	(1)
Defined benefit pension plans, deferred tax asset	153	249
Defined Benefit Plan Accumulated Other Comprehensive Income Adjustments Net Of Tax	(435)	(385)
Postretirement benefit plans, deferred net actuarial loss	(75)	(138)
Deferred Prior Service Cost (Credit) Postretirement Benefit Plans	37	49
Defined benefit pension plans, deferred tax asset	10	35
Net unrecognized periodic benefit costs for postretirement benefit plans	(28)	(54)
Foreign currency translation adjustments, gross unrealized losses	(2)	(3)
Foreign currency translation adjustments, deferred tax asset	0	1
Net unrealized losses on foreign currency translation adjustments	(2)	(2)
Accumulated other comprehensive loss	$ (811)	$ (126)	$ (101)