Outstanding Insurance Exposure - Narrative (Details) - USD ($) $ in Millions				1 Months Ended	3 Months Ended
	Jun. 05, 2019	May 09, 2019	Feb. 12, 2019	Jul. 31, 2019	Mar. 31, 2020	Feb. 28, 2020	Dec. 31, 2019	Jun. 27, 2019	Jun. 16, 2019	Jan. 14, 2019
Schedule of Insured Financial Obligations [Line Items]
Second-to-pay insured par outstanding					$ 6,200		$ 6,600
Loss mitigation securities					1,400		1,400
Residual value insurance policies exposure downgraded					1,484		1,444
Total net exposure					230,898		236,807
Net Exposure					1,178		1,141
Structured Finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure					9,528		10,061
Public Finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure					221,370		226,746
Aircraft residual value insurance (RVI) [Member]
Schedule of Insured Financial Obligations [Line Items]
Residual value insurance policies exposure downgraded					393		398
Net Exposure					$ 238		243
BIG [Member]
Schedule of Insured Financial Obligations [Line Items]
Maximum period of liquidity claims (in years)					1 year
Residual value insurance policies exposure downgraded					$ 30
Total net exposure					8,238		8,506
BIG [Member] | Structured Finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure					1,771		1,837
BIG [Member] | Public Finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure					6,467		6,669
AAA [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure					4,186		4,361
United States [Member] | RMBS [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure					3,393		3,546
United States [Member] | Structured Finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure					8,806		9,300
United States [Member] | Public Finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure					172,795		175,487
United States [Member] | BIG [Member] | RMBS [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure					1,580		1,618
United States [Member] | BIG [Member] | Structured Finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure					1,730		1,796
United States [Member] | BIG [Member] | Public Finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure					5,630		5,771
United States [Member] | AAA [Member] | Structured Finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure					1,182		1,258
United States [Member] | AAA [Member] | Public Finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure					375		381
Puerto Rico [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure					4,270		4,270
Puerto Rico [Member] | BIG [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure					4,300
U.S. Virgin Islands [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure					485
U.S. Virgin Islands [Member] | BIG [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure					219
U.S. Virgin Islands [Member] | Internal Investment Grade [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure					266
Commitment to Provide Guarantees [Member] | Structured Finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Outstanding commitments to provide guaranties					593
Commitment to Provide Guarantees [Member] | Public Finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Outstanding commitments to provide guaranties					$ 444
Minimum [Member]
Schedule of Insured Financial Obligations [Line Items]
Probability of paying more claims than being reimbursed (as a percent)					50.00%
Maximum [Member] | Capital relieve triple-X life insurance [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Exposure					$ 1,000
Commonwealth of Puerto Rico [Member]
Schedule of Insured Financial Obligations [Line Items]
Certified fiscal plan, commonwealth debt service, period		6 years
PRHTA (Highway revenue) [Member] | Puerto Rico [Member]
Schedule of Insured Financial Obligations [Line Items]
Obligations secured by taxes on crude oil, unfinished oil and derivative products					120
PRHTA [Member]
Schedule of Insured Financial Obligations [Line Items]
Certified fiscal plan, commonwealth debt service, period	6 years
Constitutionally Guaranteed [Member] | Commonwealth of Puerto Rico [Member] | Puerto Rico [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure					1,253		1,253
Fiscal plan, commonwealth general obligation bonds, litigation amount						$ 35,000			$ 35,000
Fiscal plan, commonwealth surplus available for debt service		$ 13,700
General Obligation Plan Support Agreement, Outstanding Principal Amount, Net									$ 8,000
Constitutionally Guaranteed [Member] | Commonwealth of Puerto Rico [Member] | General Obligations Bonds Issues On or After March 2012 [Member] | Puerto Rico [Member]
Schedule of Insured Financial Obligations [Line Items]
Fiscal plan, commonwealth general obligation bonds, litigation amount										$ 6,000
Fiscal plan, commonwealth surplus available for debt service					369
Constitutionally Guaranteed [Member] | Commonwealth of Puerto Rico [Member] | General Obligations Bonds Issued in or after 2011 [Member] | Puerto Rico [Member]
Schedule of Insured Financial Obligations [Line Items]
Fiscal plan, commonwealth surplus available for debt service					215
Constitutionally Guaranteed [Member] | Puerto Rico Public Buildings Authority [Member] | Puerto Rico [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure					140		140
Other Public Corporations [Member] | Puerto Rico Sales Tax Financing Corporation [Member] | Puerto Rico [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure			$ 273
Other Public Corporations [Member] | PRASA (Puerto Rico Aqueduct and Sewer Authority) [Member] | Puerto Rico [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure					373		373
Minimum period in forbearance				3 years
Debt instrument, term				40 years
Non-interest accrual period				10 years
Other Public Corporations [Member] | MFA [Member] | Puerto Rico [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure					248		248
Other Public Corporations [Member] | PREPA [Member] | Puerto Rico [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure					822		822
Fiscal plan, commonwealth contractual debt service restructuring, minimum bondholder support threshold, percent								67.00%
Pension Obligations [Member] | Commonwealth of Puerto Rico [Member] | Puerto Rico [Member]
Schedule of Insured Financial Obligations [Line Items]
Fiscal plan, commonwealth general obligation bonds, litigation amount						$ 50,000
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					$ 100		$ 105
Closed Lien Senior Bonds [Member] | Puerto Rico Sales Tax Financing Corporation [Member] | Puerto Rico [Member]
Schedule of Insured Financial Obligations [Line Items]
Financial Guaranty Insurance, Plan of Adjustment, Closed Lien Senior Bonds Received			$ 152
Subordinated Bonds [Member] | Constitutionally Guaranteed [Member] | Puerto Rico Sales Tax Financing Corporation [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