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, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ 646	$ 520	$ 537	$ 481
Total gains (losses) recognized in net income	4	0	(227)	(1)
Total gains (losses) recognized in accumulated other comprehensive loss	(1)	5	(3)	9
Purchases	40	48	369	198
Sales	(5)	(3)	(21)	(50)
Settlements	(30)	(19)	(62)	(56)
Transfers into Level III	7	4	70	20
Transfers out of Level III	(15)	(28)	(17)	(74)
Ending balance	646	527	646	527
Change in unrealized losses included in net income related to assets still held	9	(1)	27	(3)
Corporate Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	304	238	229	238
Total gains (losses) recognized in net income	0	0	1	(1)
Total gains (losses) recognized in accumulated other comprehensive loss	(1)	(1)	(3)	3
Purchases	32	11	94	72
Sales	(2)	(3)	(17)	(43)
Settlements	(30)	(14)	(60)	(50)
Transfers into Level III	6	0	65	13
Transfers out of Level III	(2)	(1)	(2)	(2)
Ending balance	307	230	307	230
Change in unrealized losses included in net income related to assets still held	0	(1)	0	(3)
Residential Mortgage-Backed Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	4	3	5	12
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	2	0	3
Sales	0	0	0	(5)
Settlements	0	0	(1)	0
Transfers into Level III	0	0	0	1
Transfers out of Level III	0	0	0	(6)
Ending balance	4	5	4	5
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	26	35	16	43
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	3	5	12	36
Sales	0	0	0	(1)
Settlements	0	(5)	(1)	(6)
Transfers into Level III	1	4	5	6
Transfers out of Level III	(13)	(27)	(15)	(66)
Ending balance	17	12	17	12
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	312	244	287	188
Total gains (losses) recognized in net income	4	0	(228)	0
Total gains (losses) recognized in accumulated other comprehensive loss	0	6	0	6
Purchases	5	30	263	87
Sales	(3)	0	(4)	(1)
Settlements	0	0	0	0
Transfers into Level III	0	0	0	0
Transfers out of Level III	0	0	0	0
Ending balance	318	280	318	280
Change in unrealized losses included in net income related to assets still held	$ 9	$ 0	$ 27	$ 0