Securities - Summary of Amortized Cost of Available-for-Sale Securities by Contractual Maturity (Details) $ in Millions	Sep. 30, 2021 USD ($)
Available-for-Sale Debt Securities:
Due within one year	$ 95
Due from one to five years	646
Due from five to ten years	1,065
Due after ten years	4,092
Total debt securities available for sale	5,898
Mortgage-Related Securities
Available-for-Sale Debt Securities:
Due within one year	26
Due from one to five years	193
Due from five to ten years	197
Due after ten years	2,566
Total debt securities available for sale	$ 2,982
Available-for-Sale Securities, Average Yield
Due within one year, Average Yield	2.72%
Due from one to five years, Average Yield	3.25%
Due from five to ten years, Average Yield	2.52%
Due after ten years, Average Yield	1.85%
Total securities available for sale, Average Yield	1.99%
U.S. Government and GSE obligations
Available-for-Sale Debt Securities:
Due within one year	$ 69
Due from one to five years	22
Due from five to ten years	317
Due after ten years	1,070
Total debt securities available for sale	$ 1,478
Available-for-Sale Securities, Average Yield
Due within one year, Average Yield	0.17%
Due from one to five years, Average Yield	3.52%
Due from five to ten years, Average Yield	1.58%
Due after ten years, Average Yield	1.54%
Total securities available for sale, Average Yield	1.51%
State, County, and Municipal
Available-for-Sale Debt Securities:
Due from five to ten years	$ 19
Due after ten years	6
Total debt securities available for sale	$ 25
Available-for-Sale Securities, Average Yield
Due from five to ten years, Average Yield	3.52%	[1]
Due after ten years, Average Yield	3.33%	[1]
Total securities available for sale, Average Yield	3.48%	[1]
Other Debt Securities
Available-for-Sale Debt Securities:
Due from one to five years	$ 403	[2]
Due from five to ten years	523	[2]
Due after ten years	509	[2]
Total debt securities available for sale	$ 1,435	[2]
Available-for-Sale Securities, Average Yield
Due from one to five years, Average Yield	1.62%
Due from five to ten years, Average Yield	2.26%
Due after ten years, Average Yield	1.18%
Total securities available for sale, Average Yield	1.70%

[1] Not presented on a tax-equivalent basis.

[2] Includes corporate bonds, capital trust notes, foreign notes and asset-backed securities.