Outstanding Insurance Exposure - Amortization Schedule of Puerto Rico Net Par Outstanding and Net Debt Service Outstanding (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Estimated Net Par Amortization [Abstract]
Total	$ 233,075	$ 236,807
Estimated Net Debt Service Amortization [Abstract]
Total	364,507	374,130
Puerto Rico
Estimated Net Par Amortization [Abstract]
2020 (October 1 - December 31)	0
2021 (January 1 - March 31)	0
2021 (April 1 - June 30)	0
2021 (July 1 - September 30)	153
2021 (October 1 - December 31)	0
Subtotal 2021	153
2022	176
2023	206
2024	223
2025-2029	1,173
2030-2034	1,052
2035-2039	763
2040-2044	104
2045-2047	246
Total	4,096	$ 4,270
Estimated Net Debt Service Amortization [Abstract]
2020 (October 1 - December 31)	3
2021 (January 1 - March 31)	101
2021 (April 1 - June 30)	3
2021 (July 1 - September 30)	254
2021 (October 1 - December 31)	3
Subtotal 2021	361
2022	375
2023	396
2024	403
2025-2029	1,894
2030-2034	1,527
2035-2039	942
2040-2044	179
2045-2047	272
Total	$ 6,352