Outstanding Exposure - Amortization Schedule of Puerto Rico Net Par Outstanding and Net Debt Service Outstanding (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Estimated Net Par Amortization [Abstract]
Total	$ 246,940	$ 264,952
Estimated Net Debt Service Amortization [Abstract]
Total	378,693	401,118
Puerto Rico [Member]
Estimated Net Par Amortization [Abstract]
2018 (October 1 - December 31)	0
2019 (January 1 - March 31)	0
2019 (April 1 - June 30)	0
2019 (July 1 - September 30)	224
2019 (October 1 - December 31)	0
Subtotal 2019	224
2020	285
2021	147
2022	137
2023-2027	1,229
2028-2032	812
2033-2037	1,217
2038-2042	453
2043-2047	263
Total	4,767	$ 4,966
Estimated Net Debt Service Amortization [Abstract]
2018 (October 1 - December 31)	3
2019 (January 1 - March 31)	117
2019 (April 1 - June 30)	3
2019 (July 1 - September 30)	341
2019 (October 1 - December 31)	3
Subtotal 2019	464
2020	516
2021	364
2022	345
2023-2027	2,128
2028-2032	1,436
2033-2037	1,572
2038-2042	602
2043-2047	316
Total	$ 7,746