Outstanding Exposure - Amortization Schedule of Puerto Rico BIG Net Par Outstanding and BIG Net Debt Service Outstanding (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Estimated BIG Net Par Amortization [Abstract]
Net Par Outstanding	$ 264,952	$ 296,318
Estimated BIG Net Debt Service Amortization [Abstract]
Total	401,118	437,535
Puerto Rico [Member]
Estimated BIG Net Par Amortization [Abstract]
2018 (January 1 - March 31)	0
2018 (April 1 - June 30)	0
2018 (July 1 - September 30)	200
2018 (October 1 - December 31)	0
Subtotal 2018	200
2019	223
2020	285
2021	147
2022	137
2023-2027	1,229
2028-2032	812
2033-2037	1,217
2038-2042	453
2043-2047	263
Net Par Outstanding	4,966	$ 4,786
Estimated BIG Net Debt Service Amortization [Abstract]
2018 (January 1 - March 31)	123
2018 (April 1 - June 30)	3
2018 (July 1 - September 30)	322
2018 (October 1 - December 31)	3
Subtotal 2018	451
2019	464
2020	516
2021	364
2022	345
2023-2027	2,129
2028-2032	1,436
2033-2037	1,572
2038-2042	602
2043-2047	316
Total	$ 8,195