Loans and Allowance for Credit Losses - Investments by Credit Quality (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	$ 32,797	$ 27,925
Investment grade
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	26,899	22,583
Speculative
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	5,563	5,224
Special mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	156	67
Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	164	34
Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	15	17
Commercial and Financial Segment
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	30,413	25,829
Commercial and Financial Segment | Investment grade
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	24,936	20,859
Commercial and Financial Segment | Speculative
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	5,180	4,852
Commercial and Financial Segment | Special mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	118	67
Commercial and Financial Segment | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	164	34
Commercial and Financial Segment | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	15	17
Commercial Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	2,384	2,096
Commercial Real Estate | Investment grade
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	1,963	1,724
Commercial Real Estate | Speculative
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	383	372
Commercial Real Estate | Special mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	38	0
Commercial Real Estate | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	0	0
Commercial Real Estate | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	0	0
Geographic Distribution, Domestic
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	22,650	21,132
Geographic Distribution, Domestic | Commercial and Financial Segment
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	20,266	19,036
Geographic Distribution, Domestic | Commercial and Financial Segment | Investment grade
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	16,343	15,489
Geographic Distribution, Domestic | Commercial and Financial Segment | Speculative
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	3,664	3,446
Geographic Distribution, Domestic | Commercial and Financial Segment | Special mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	118	67
Geographic Distribution, Domestic | Commercial and Financial Segment | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	141	34
Geographic Distribution, Domestic | Commercial Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	2,384	2,096
Geographic Distribution, Domestic | Commercial Real Estate | Investment grade
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	1,963	1,723
Geographic Distribution, Domestic | Commercial Real Estate | Speculative
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	383	373
Geographic Distribution, Domestic | Commercial Real Estate | Special mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	38
Geographic Distribution, Domestic | Loans to investment funds
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	12,367	11,531
Overdrafts	$ 3,814	$ 2,982