Accumulated Other Comprehensive Loss (Reconciliation Of The Components Of Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Investments, Accumulated Gross Unrealized Gain, before Tax	$ 510	$ 379
Investments, Accumulated Gross Unrealized Loss, before Tax	(729)	(121)
Investments, net pretax unrealized gains (losses) excluding non-credit component of other-than-temporary impairments	(219)	258
Deferred tax (liability) asset	51	(61)
Net unrealized gains (losses) on investments excluding non-credit component of other-than-temporary impairments	(168)	197
Non-credit component of other than temporary impairments on investments, unrealized losses	(44)	(3)
Non-credit component of other than temporary impairments on investments, deferred tax asset	10	1
Net unrealized non-credit component of other than temporary impairments on investments	(34)	(2)
Unrealized Gain (Loss) on Interest Rate Cash Flow Hedges, Pretax, Accumulated Other Comprehensive Income (Loss)	(327)	(308)
Cash flow hedges, deferred tax asset	68	65
AOCI, Cash Flow Hedge, Cumulative Gain (Loss), after Tax	(259)	(243)
Defined benefit pension plans, deferred net actuarial loss	(724)	(744)
Defined benefit pension plans, deferred prior service credits	0	(1)
Defined benefit pension plans, deferred tax asset	185	191
Net unrecognized periodic benefit costs for defined benefit pension plans	(539)	(554)
Postretirement benefit plans, deferred net actuarial loss	(25)	(57)
Postretirement beneft plans, prior service costs	18	31
Postretirement benefit plans, deferred tax asset	2	7
Net unrecognized periodic benefit costs for postretirement benefit plans	(5)	(19)
Foreign currency translation adjustments, gross unrealized losses	(4)	(3)
Foreign currency translation adjustments, deferred tax asset	1	1
Net unrealized losses on foreign currency translation adjustments	(3)	(2)
Accumulated other comprehensive loss	$ (1,008)	$ (623)	$ (296)