Fair Value (Reconciliation Of The Beginning And Ending Balances Of Assets Measured At Fair Value On A Recurring Basis Using Level III Inputs) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ 616	$ 646	$ 623	$ 537
Total gains (losses) recognized in net income	(8)	4	(12)	(227)
Total gains (losses) recognized in accumulated other comprehensive loss	12	(1)	14	(3)
Purchases	53	40	139	369
Sales	(28)	(5)	(59)	(21)
Settlements	(18)	(30)	(61)	(62)
Transfers into Level III	4	7	7	70
Transfers out of Level III	0	(15)	(20)	(17)
Ending balance	631	646	631	646
Change in unrealized losses included in net income related to assets still held	(4)	9	(4)	27
Corporate Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	297	304	287	229
Total gains (losses) recognized in net income	(3)	0	(7)	1
Total gains (losses) recognized in accumulated other comprehensive loss	12	(1)	14	(3)
Purchases	28	32	91	94
Sales	(9)	(2)	(11)	(17)
Settlements	(18)	(30)	(58)	(60)
Transfers into Level III	4	6	4	65
Transfers out of Level III	0	(2)	(9)	(2)
Ending balance	311	307	311	307
Change in unrealized losses included in net income related to assets still held	0	0	0	0
Residential Mortgage-Backed Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	3	4	6	5
Total gains (losses) recognized in net income	0	0	0	0
Total gains (losses) recognized in accumulated other comprehensive loss	0	0	0	0
Purchases	0	0	0	0
Sales	0	0	0	0
Settlements	0	0	(1)	(1)
Transfers into Level III	0	0	0	0
Transfers out of Level III	0	0	(2)	0
Ending balance	3	4	3	4
Change in unrealized losses included in net income related to assets still held	0	0	0	0
Other Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	11	26	17	16
Total gains (losses) recognized in net income	0	0	0	0
Total gains (losses) recognized in accumulated other comprehensive loss	0	0	0	0
Purchases	0	3	2	12
Sales	0	0	0	0
Settlements	0	0	(2)	(1)
Transfers into Level III	0	1	3	5
Transfers out of Level III	0	(13)	(9)	(15)
Ending balance	11	17	11	17
Change in unrealized losses included in net income related to assets still held	0	0	0	0
Equity Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	305	312	313	287
Total gains (losses) recognized in net income	(5)	4	(5)	(228)
Total gains (losses) recognized in accumulated other comprehensive loss	0	0	0	0
Purchases	25	5	46	263
Sales	(19)	(3)	(48)	(4)
Settlements	0	0	0	0
Transfers into Level III	0	0	0	0
Transfers out of Level III	0	0	0	0
Ending balance	306	318	306	318
Change in unrealized losses included in net income related to assets still held	$ (4)	$ 9	$ (4)	$ 27