Offsetting Assets and Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Offsetting [Abstract]
Federal funds sold and security resell agreements, Gross amounts recognized	$ 6,457	$ 694
Federal funds sold and security resell agreements, Gross amounts offset in the balance sheet	(692)	(210)
Federal funds sold and security resell agreements, Net amounts presented in balance sheet	5,765	484
Federal funds sold and security resell agreements, financial instruments	0	0
Federal funds sold and security resell agreements, cash collateral received/pledged	0	0
Federal funds sold and security resell agreements, Net amount	5,765	484
Derivative assets, Gross amounts recognized	418	153
Derivative assets, Gross amounts offset in the balance sheet	0	0
Derivative assets, Net amounts presented in balance sheet	418	153
Derivatives asset, Financial instruments	(6)	(6)
Derivatives asset, Cash collateral received/pledged	(3)	0
Derivative assets, Net amount	409	147
Total assets, Gross amounts recognized	6,875	847
Total assets, Gross amounts offset in the balance sheet	(692)	(210)
Total assets, Net amounts presented in the balance sheet	6,183	637
Total assets, Financial instruments	(6)	(6)
Total assets, Cash collateral received/pledged	(3)	0
Total assets, Net amounts	6,174	631
Federal funds purchased and other short-term borrowings, Gross amounts recognized	2,264	2,263
Federal funds purchased and other short-term borrowings, Gross amounts offset in balance sheet	(692)	(210)
Federal funds purchased and other short-term borrowings, Net amounts presented in balance sheet	1,572	2,053
Federal funds purchased and other short-term borrowings, Financial instruments	0	0
Federal funds purchased and other short-term borrowings, Cash collateral received/pledged	0	0
Federal funds purchased and other short-term borrowings, Net amount	1,572	2,053
Derivative liabilities, Gross amounts recognized	38	19
Derivative liabilities, Gross amounts offset in balance sheet	0	0
Derivative liabilities, Net amounts presented in balance sheet	38	19
Derivative liabilities, Financial instrument	(6)	(6)
Derivative liabilities, Cash collateral received/pledged	(26)	(10)
Derivative liabilities, Net amount	6	3
Total liabilities, Gross amounts recognized	2,302	2,282
Total liabilities, Gross amounts offset in balance sheet	(692)	(210)
Total liabilities, Net amounts presented in the balance sheet	1,610	2,072
Total liabilities, Financial instruments	(6)	(6)
Total liabilities, Cash collateral received/pledged	(26)	(10)
Total liabilities, Net amount	$ 1,578	$ 2,056