Credit Quality And Allowance For Credit Losses (Changes In The Allowance For Credit Losses On Lending-Related Commitments) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Financing Receivable, Allowance for Credit Loss [Line Items]
Provision for credit losses on lending-related commitments	$ (8)	$ (35)	$ (44)	$ 13	$ (16)	$ 0	$ (12)	$ 29	$ (74)	$ 1	$ (74)
Lending-related commitments
Financing Receivable, Allowance for Credit Loss [Line Items]
Balance at beginning of period				$ 30			$ 42		30	42	41
Provision for credit losses on lending-related commitments									1	(12)	1
Balance at end of period	$ 31				$ 30			$ 42	$ 31	$ 30	$ 42