Outstanding Exposure - Expected Amortization of Net Par Outstanding (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Expected Amortization of Net Par Outstanding [Abstract]
0 to 5 years	$ 67,628
5 to 10 years	52,606
10 to 15 years	45,552
15 to 20 years	35,205
20 years and above	40,811
Net Par Outstanding	241,802	$ 264,952
Public Finance [Member]
Expected Amortization of Net Par Outstanding [Abstract]
0 to 5 years	61,889
5 to 10 years	50,296
10 to 15 years	44,188
15 to 20 years	33,709
20 years and above	40,583
Net Par Outstanding	230,665	252,314
Structured Finance [Member]
Expected Amortization of Net Par Outstanding [Abstract]
0 to 5 years	5,739
5 to 10 years	2,310
10 to 15 years	1,364
15 to 20 years	1,496
20 years and above	228
Net Par Outstanding	$ 11,137	$ 12,638