Outstanding Insurance Exposure - Expected Amortization of Net Par Outstanding (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Expected Amortization of Net Par Outstanding [Abstract]
0 to 5 years	$ 59,380
5 to 10 years	50,352
10 to 15 years	44,818
15 to 20 years	35,518
20 years and above	46,739
Net Par Outstanding, Total	236,807	$ 241,802
Public Finance [Member]
Expected Amortization of Net Par Outstanding [Abstract]
0 to 5 years	55,219
5 to 10 years	48,500
10 to 15 years	42,901
15 to 20 years	33,820
20 years and above	46,306
Net Par Outstanding, Total	226,746	230,665
Structured Finance [Member]
Expected Amortization of Net Par Outstanding [Abstract]
0 to 5 years	4,161
5 to 10 years	1,852
10 to 15 years	1,917
15 to 20 years	1,698
20 years and above	433
Net Par Outstanding, Total	$ 10,061	$ 11,137