Fair Value Measurements - Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Millions	Sep. 30, 2021		Dec. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	$ 5,914	[1]	$ 5,845	[2]
Total equity securities	16		32
Total securities	5,914		5,845
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	5,898		5,814
Total equity securities	16		31
Total securities	5,914		5,845
Fair Value, Measurements, Recurring | Preferred Stock
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total equity securities			15
Fair Value, Measurements, Recurring | Mutual Fund
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total equity securities	16		16
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	65		65
Total equity securities			15
Total securities	65		80
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Preferred Stock
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total equity securities			15
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	5,833		5,749
Total equity securities	16		16
Total securities	5,849		5,765
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Mutual Fund
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total equity securities	16		16
Fair Value, Measurements, Recurring | Mortgage-Related Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	2,979		3,038
Fair Value, Measurements, Recurring | Mortgage-Related Securities | GSE Certificates
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	1,130		1,209
Fair Value, Measurements, Recurring | Mortgage-Related Securities | GSE CMOs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	1,849		1,829
Fair Value, Measurements, Recurring | Mortgage-Related Securities | Municipal Bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	25
Fair Value, Measurements, Recurring | Mortgage-Related Securities | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale			3,038
Fair Value, Measurements, Recurring | Mortgage-Related Securities | Quoted Prices in Active Markets for Identical Assets (Level 1) | GSE Certificates
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale			1,209
Fair Value, Measurements, Recurring | Mortgage-Related Securities | Quoted Prices in Active Markets for Identical Assets (Level 1) | GSE CMOs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale			1,829
Fair Value, Measurements, Recurring | Mortgage-Related Securities | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	2,979
Fair Value, Measurements, Recurring | Mortgage-Related Securities | Significant Other Observable Inputs (Level 2) | GSE Certificates
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	1,130
Fair Value, Measurements, Recurring | Mortgage-Related Securities | Significant Other Observable Inputs (Level 2) | GSE CMOs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	1,849
Fair Value, Measurements, Recurring | Mortgage-Related Securities | Significant Other Observable Inputs (Level 2) | Capital Trust Notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	95
Fair Value, Measurements, Recurring | Other Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	2,919		2,776
Fair Value, Measurements, Recurring | Other Securities | U.S. Treasury Obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	65		65
Fair Value, Measurements, Recurring | Other Securities | GSE Debentures
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	1,372		1,158
Fair Value, Measurements, Recurring | Other Securities | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	495		526
Fair Value, Measurements, Recurring | Other Securities | Municipal Bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale			27
Fair Value, Measurements, Recurring | Other Securities | Corporate Bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	841		883
Fair Value, Measurements, Recurring | Other Securities | Foreign Notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	26		26
Fair Value, Measurements, Recurring | Other Securities | Capital Trust Notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	95		91
Fair Value, Measurements, Recurring | Other Securities | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	65		65
Fair Value, Measurements, Recurring | Other Securities | Quoted Prices in Active Markets for Identical Assets (Level 1) | U.S. Treasury Obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	65		65
Fair Value, Measurements, Recurring | Other Securities | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	2,854		2,711
Fair Value, Measurements, Recurring | Other Securities | Significant Other Observable Inputs (Level 2) | GSE Certificates
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale			1,158
Fair Value, Measurements, Recurring | Other Securities | Significant Other Observable Inputs (Level 2) | GSE Debentures
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	1,372
Fair Value, Measurements, Recurring | Other Securities | Significant Other Observable Inputs (Level 2) | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	495		526
Fair Value, Measurements, Recurring | Other Securities | Significant Other Observable Inputs (Level 2) | Municipal Bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	25		27
Fair Value, Measurements, Recurring | Other Securities | Significant Other Observable Inputs (Level 2) | Corporate Bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	841		883
Fair Value, Measurements, Recurring | Other Securities | Significant Other Observable Inputs (Level 2) | Foreign Notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	$ 26		26
Fair Value, Measurements, Recurring | Other Securities | Significant Other Observable Inputs (Level 2) | Capital Trust Notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale			$ 91

[1] Excludes accrued interest receivable of $14 million included in other assets in the Consolidated Statements of Condition.

[2] Excludes accrued interest receivable of $15 million included in other assets in the Consolidated Statements of Condition.