Accounting and Reporting Developments (Details) - USD ($) $ in Millions		9 Months Ended
	Jan. 01, 2020	Sep. 30, 2020		Sep. 30, 2019	Jun. 30, 2020	Dec. 31, 2019		Jun. 30, 2019	Dec. 31, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201613Member	us-gaap:AccountingStandardsUpdate201613Member		us-gaap:AccountingStandardsUpdate201602Member
ALLL and reserve for unfunded commitments	$ 33	$ 2,574	[1]	$ 1,143	$ 2,696	$ 1,202	[1]	$ 1,115	$ 1,103
Impact of cumulative effect of change in accounting principles		18,010				$ 18,315
Carrying value of loans and leases evaluated for ALLL		$ 1
Retained Earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
ALLL and reserve for unfunded commitments	653
Impact of cumulative effect of change in accounting principles	472
Amount of ALLL on purchased financial assets	$ 33

[1] Includes $61 and $74 of other short-term investments, $887 and $1,354 of portfolio loans and leases, $(9) and $(7) of ALLL, $5 and $8 of other assets, $2 and $2 of other liabilities, and $786 and $1,253 of long-term debt from consolidated VIEs that are included in their respective captions above at September 30, 2020 and December 31, 2019, respectively. For further information refer to Note 13.