Outstanding Insurance Exposure - Narrative (Details)					2 Months Ended	12 Months Ended
	Jun. 27, 2019	Jun. 05, 2019	May 09, 2019 USD ($)	Feb. 12, 2019 USD ($)	Feb. 28, 2020 Earthquake Richter_Magnitude	Dec. 31, 2019 USD ($)	Feb. 09, 2020 USD ($)	Sep. 27, 2019 USD ($)	Jan. 14, 2019 USD ($)	Dec. 31, 2018 USD ($)
Schedule of Insured Financial Obligations [Line Items]
Second-to pay insured par outstanding						$ 6,600,000,000				$ 6,700,000,000
Net par amount outstanding						236,807,000,000				241,802,000,000
Structured Finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding						10,061,000,000				11,137,000,000
Public Finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding						$ 226,746,000,000				230,665,000,000
BIG [Member]
Schedule of Insured Financial Obligations [Line Items]
Maximum period of liquidity claims (in years)						1 year
Loss mitigation securities held in investment portfolios excluding from net par						$ 1,400,000,000				1,900,000,000
Net par amount outstanding						8,506,000,000				10,160,000,000
BIG [Member] | Structured Finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding						1,837,000,000				2,731,000,000
BIG [Member] | Public Finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding						6,669,000,000				7,429,000,000
Puerto Rico [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding						4,270,000,000				4,767,000,000
Puerto Rico [Member] | Public Finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding						4,270,000,000
Puerto Rico [Member] | BIG [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding						4,300,000,000
VIRGIN ISLANDS, US
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding						485,000,000
VIRGIN ISLANDS, US | BIG [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding						218,000,000
VIRGIN ISLANDS, US | Internal Investment Grade [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding						267,000,000
Commitment to Provide Guarantees [Member] | Structured Finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Outstanding commitments to provide guaranties						610,000,000
Commitment to Provide Guarantees [Member] | Public Finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Outstanding commitments to provide guaranties						$ 301,000,000
Minimum [Member]
Schedule of Insured Financial Obligations [Line Items]
Probability of paying more claims than being reimbursed (as a percent)						50.00%
Commonwealth of Puerto Rico - General Obligation Bonds [Member]
Schedule of Insured Financial Obligations [Line Items]
Commonwealth debt service, period			6 years
PRHTA (Transportation revenue) [Member]
Schedule of Insured Financial Obligations [Line Items]
Commonwealth debt service, period		6 years
PRHTA (Highway revenue) [Member] | Puerto Rico [Member]
Schedule of Insured Financial Obligations [Line Items]
Insured financial obligations, secured by pledges						$ 120,000,000
Constitutionally Guaranteed [Member] | Commonwealth of Puerto Rico - General Obligation Bonds [Member] | Puerto Rico [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding						1,253,000,000				1,340,000,000
Fiscal plan budget surplus			$ 13,700,000,000
Litigation amount								$ 35,000,000,000
Constitutionally Guaranteed [Member] | Commonwealth of Puerto Rico - General Obligation Bonds [Member] | General Obligations Bonds Issues On or After March 2012 [Member] | Puerto Rico [Member]
Schedule of Insured Financial Obligations [Line Items]
Fiscal plan budget surplus						369,000,000
Litigation amount									$ 6,000,000,000
Constitutionally Guaranteed [Member] | Commonwealth of Puerto Rico - General Obligation Bonds [Member] | General Obligations Bonds Issued in or after 2011 [Member] | Puerto Rico [Member]
Schedule of Insured Financial Obligations [Line Items]
Fiscal plan budget surplus						215,000,000
Constitutionally Guaranteed [Member] | PREPA [Member] | Puerto Rico [Member]
Schedule of Insured Financial Obligations [Line Items]
New securitization percent of par	67.00%
Constitutionally Guaranteed [Member] | Puerto Rico Public Buildings Authority [Member] | Puerto Rico [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding						140,000,000				142,000,000
Pension Obligations [Member] | Commonwealth of Puerto Rico - General Obligation Bonds [Member] | Puerto Rico [Member]
Schedule of Insured Financial Obligations [Line Items]
Litigation amount								$ 50,000,000,000
Public Corporations - Certain Revenues Potentially Subject to Clawback [Member] | PRHTA (Transportation revenue) [Member] | Puerto Rico [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding						811,000,000				844,000,000
Public Corporations - Certain Revenues Potentially Subject to Clawback [Member] | PRHTA (Highway revenue) [Member] | Puerto Rico [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding						454,000,000				475,000,000
Public Corporations - Certain Revenues Potentially Subject to Clawback [Member] | PRCCDA [Member] | Puerto Rico [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding						152,000,000				152,000,000
Public Corporations - Certain Revenues Potentially Subject to Clawback [Member] | PRIFA [Member] | Puerto Rico [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding						16,000,000				16,000,000
Other Public Corporations [Member] | PREPA [Member] | Puerto Rico [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding						822,000,000				848,000,000
Other Public Corporations [Member] | Puerto Rico Municipal Finance Authority [Member] | Puerto Rico [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding						248,000,000				303,000,000
Other Public Corporations [Member] | PRASA [Member] | Puerto Rico [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding						$ 373,000,000				373,000,000
Minimum forbearance, period						3 years
Debt Instrument, term						40 years
Non-interest accrual period						10 years
Other Public Corporations [Member] | COFINA [Member] | Puerto Rico [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding				$ 273,000,000		$ 0
Other Public Corporations [Member] | U of PR [Member] | Puerto Rico [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding						1,000,000				1,000,000
Subsequent Event [Member] | Minimum [Member]
Schedule of Insured Financial Obligations [Line Items]
Number of earthquakes | Earthquake					11
Number of earthquake, Richter magnitude scale | Richter_Magnitude					5
Subsequent Event [Member] | Constitutionally Guaranteed [Member] | Commonwealth of Puerto Rico - General Obligation Bonds [Member] | Puerto Rico [Member]
Schedule of Insured Financial Obligations [Line Items]
Outstanding principal amount, net							$ 8,000,000,000
Litigation amount							$ 35,000,000,000
Closed Lien Senior Bonds [Member] | COFINA [Member] | Puerto Rico [Member]
Schedule of Insured Financial Obligations [Line Items]
Financial guaranty insurance, plan of adjustment, closed lien senior bonds received				$ 152,000,000
Subordinated Bonds [Member] | Constitutionally Guaranteed [Member] | COFINA [Member] | Puerto Rico [Member]
Schedule of Insured Financial Obligations [Line Items]
Expected repayments of debt, percent				60.00%
COFINA Exchange Senior Bonds [Member] | Puerto Rico [Member]
Schedule of Insured Financial Obligations [Line Items]
Plan of adjustment, closed lien senior bonds received, fair value				$ 139,000,000
External Credit Rating, Non Investment Grade [Member] | Below Investment Grade, Rating Withdrawn Or Not Rated Reinsurer [Member]
Schedule of Insured Financial Obligations [Line Items]
Second-to pay insured par outstanding						$ 105,000,000				$ 111,000,000