Representations and Warranties Obligations and Corporate Guarantees - Unresolved Repurchase Claims by Counterparty, net of duplicate claims (Details) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Loss Contingencies [Line Items]
Unresolved repurchase claims, net of duplicated claims	$ 18,265	$ 18,277
Outstanding claims with review	11,900	11,900
Outstanding claims without review	4,800	4,800
Private-label securitization trustees, whole-loan investors, including third-party securitization sponsors and other
Loss Contingencies [Line Items]
Unresolved repurchase claims, net of duplicated claims	16,678	16,685
Monolines
Loss Contingencies [Line Items]
Unresolved repurchase claims, net of duplicated claims	1,583	1,583
GSEs
Loss Contingencies [Line Items]
Unresolved repurchase claims, net of duplicated claims	$ 4	$ 9