Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (g)
-URI http://asc.fasb.org/extlink&oid=121611835&loc=SL6953423-111524

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 30
-Section 50
-Paragraph 2
-Subparagraph (b)(1)(ii)
-URI http://asc.fasb.org/extlink&oid=121614798&loc=d3e15032-111544

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=121611835&loc=SL6953423-111524

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section S99
-Paragraph 4
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-URI http://asc.fasb.org/extlink&oid=27010918&loc=d3e74567-122707

Name:	us-gaap_LoansAndLeasesReceivableAllowance
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Loans and Allowance for Loan Losses - Allowance for Loan Losses and Related Loan Balances by Portfolio Segment (Details) - USD ($) $ in Millions	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019
Loan losses allowance
Total allowance for loan losses	$ 858	$ 1,055	$ 1,273	$ 1,452	$ 1,152	$ 538
Loans held for investment:
Loans held for investment	78,567		82,166
Commercial
Loan losses allowance
Total allowance for loan losses	558	708		932	679
Loans held for investment:
Loans held for investment	50,134		50,149
Consumer
Loan losses allowance
Total allowance for loan losses	300	$ 347		$ 520	$ 473
Loans held for investment:
Loans held for investment	$ 28,433		32,017
Commercial Loans \| Commercial
Loan losses allowance
Total allowance for loan losses			851			354
Consumer Loans \| Consumer
Loan losses allowance
Total allowance for loan losses			$ 422			$ 184