Investment Securities - Credit Quality Indicators (Details) - USD ($) $ in Millions	Mar. 31, 2022	Dec. 31, 2021
Financing Receivable, Credit Quality Indicator [Line Items]
Held-to-maturity securities, amortized cost	$ 98,713	$ 98,202
Municipal bonds and notes
Financing Receivable, Credit Quality Indicator [Line Items]
Held-to-maturity securities, amortized cost	7,484	7,157
Municipal bonds and notes | Aaa
Financing Receivable, Credit Quality Indicator [Line Items]
Held-to-maturity securities, amortized cost	4,141	3,774
Municipal bonds and notes | Aa1
Financing Receivable, Credit Quality Indicator [Line Items]
Held-to-maturity securities, amortized cost	1,991	2,031
Municipal bonds and notes | Aa2
Financing Receivable, Credit Quality Indicator [Line Items]
Held-to-maturity securities, amortized cost	1,153	1,154
Municipal bonds and notes | Aa3
Financing Receivable, Credit Quality Indicator [Line Items]
Held-to-maturity securities, amortized cost	172	172
Municipal bonds and notes | A1
Financing Receivable, Credit Quality Indicator [Line Items]
Held-to-maturity securities, amortized cost	27	26
Corporate bonds
Financing Receivable, Credit Quality Indicator [Line Items]
Held-to-maturity securities, amortized cost	711	712
Corporate bonds | Aaa
Financing Receivable, Credit Quality Indicator [Line Items]
Held-to-maturity securities, amortized cost	39	39
Corporate bonds | Aa2
Financing Receivable, Credit Quality Indicator [Line Items]
Held-to-maturity securities, amortized cost	42	42
Corporate bonds | Aa3
Financing Receivable, Credit Quality Indicator [Line Items]
Held-to-maturity securities, amortized cost	105	105
Corporate bonds | A1
Financing Receivable, Credit Quality Indicator [Line Items]
Held-to-maturity securities, amortized cost	283	251
Corporate bonds | A2
Financing Receivable, Credit Quality Indicator [Line Items]
Held-to-maturity securities, amortized cost	231	264
Corporate bonds | Moody's, A3 Rating
Financing Receivable, Credit Quality Indicator [Line Items]
Held-to-maturity securities, amortized cost	$ 11	$ 11