Fair Value of Assets and Liabilities - Nonrecurring Fair Value Measurements (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale	$ 405	$ 14
Loans, net of unearned income	58,232	31,061
Non Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans, net of unearned income	77	42	$ 48
Other real estate owned (OREO)	15	16	22
Other assets	9	11	9
Net gains (losses) loans, net of unearned income	(12)	(7)	(1)
Net gains (losses) other real estate owned	(1)	(1)	(2)
Net gains (losses) other assets	(2)	(2)	(5)
Net gains (losses) financial assets	(18)	(12)	(12)
Non Recurring | Other Consumer Loans Class
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale			19
Net gains (losses) loans held-for-sale			(2)
Non Recurring | SBAs and USDA
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale	509	494	578
Net gains (losses) loans held-for-sale	(3)	(2)	(2)
Non Recurring | First Mortgages
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale	1	1	1
Net gains (losses) loans held-for-sale	0	0	0
Non Recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans, net of unearned income	0	0	0
Other real estate owned (OREO)	0	0	0
Other assets	0	0	0
Non Recurring | Level 1 | Other Consumer Loans Class
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale			0
Non Recurring | Level 1 | SBAs and USDA
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale	0	0	0
Non Recurring | Level 1 | First Mortgages
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale	0	0	0
Non Recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans, net of unearned income	0	0	0
Other real estate owned (OREO)	0	0	0
Other assets	0	0	0
Non Recurring | Level 2 | Other Consumer Loans Class
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale			19
Non Recurring | Level 2 | SBAs and USDA
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale	508	493	577
Non Recurring | Level 2 | First Mortgages
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale	0	0	0
Non Recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans, net of unearned income	77	42	48
Other real estate owned (OREO)	15	16	22
Other assets	9	11	9
Non Recurring | Level 3 | Other Consumer Loans Class
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale			0
Non Recurring | Level 3 | SBAs and USDA
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale	1	1	1
Non Recurring | Level 3 | First Mortgages
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale	$ 1	$ 1	$ 1