Fair Value (Fair Value Option - Changes in Fair Value) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Loans held for sale | Residential mortgage loans held for sale
Fair Value, Option, Quantitative Disclosures [Line Items]
Gains (losses) - FVO: changes in fair value	$ 16	$ 46
Loans held for sale | Commercial mortgage loans held for sale
Fair Value, Option, Quantitative Disclosures [Line Items]
Gains (losses) - FVO: changes in fair value	20	48
Loans
Fair Value, Option, Quantitative Disclosures [Line Items]
Gains (losses) - FVO: changes in fair value	14	18
Other assets
Fair Value, Option, Quantitative Disclosures [Line Items]
Gains (losses) - FVO: changes in fair value	$ 14	$ (36)