Commitments and Contingencies (Commitments to Extend/Purchase) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commitments to purchase			$ 9,702		$ 10,058
First Mortgage [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Purchased during period	$ 4,000	$ 2,700	6,800	$ 4,900
Commitments to purchase			2,575		1,917
HELOCs [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Purchased during period	114	$ 133	213	$ 240
Home Equity Loans and Lines of Credit Pledged Asset Lines and Other Lines of Credit [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commitments to extend credit related to unused HELOCs, PALs, and other lines of credit	$ 7,127		$ 7,127		$ 8,141