Fair Value Measurements - Assets Measured at Fair Value on Nonrecurring Basis (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Dec. 31, 2021
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale	$ 3,154		$ 4,920
Total assets at fair value	3,175		4,936
Net gains (losses) on loan sales	45	$ 227
Loans held-for-sale
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets at fair value	3,154		4,920
Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets at fair value	387		176
Net gains (losses) on loan sales	(10)		(7)
Nonrecurring | Loans held-for-sale
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale	293		116
Fair value gains (losses) on loans	(1)		(1)
Nonrecurring | Commercial loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value gains (losses) on loans	0		0
Commercial Loans Held-For-Sale, Fair Value Disclosure	18		18
Nonrecurring | Impaired residential first mortgage loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans held-for-investment	72		36
Fair value gains (losses) on loans	(8)		(5)
Nonrecurring | Repossessed assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Repossessed assets	4		6
Fair value gains (losses) on repossessed assets	(1)		(1)
Nonrecurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets at fair value	293		116
Nonrecurring | Level 2 | Loans held-for-sale
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale	293		116
Nonrecurring | Level 2 | Commercial loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Commercial Loans Held-For-Sale, Fair Value Disclosure	0		0
Nonrecurring | Level 2 | Impaired residential first mortgage loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans held-for-investment	0		0
Nonrecurring | Level 2 | Repossessed assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Repossessed assets	0		0
Nonrecurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets at fair value	94		60
Nonrecurring | Level 3 | Loans held-for-sale
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale	0		0
Nonrecurring | Level 3 | Commercial loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Commercial Loans Held-For-Sale, Fair Value Disclosure	18		18
Nonrecurring | Level 3 | Impaired residential first mortgage loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans held-for-investment	72		36
Nonrecurring | Level 3 | Repossessed assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Repossessed assets	$ 4		$ 6