Assumption of Insured Portfolio and Business Combinations - Assets and Liabilities Assumed (Details) - USD ($) $ in Millions	Jan. 10, 2017	Jul. 01, 2016
CIFG Holding Inc. [Member]
Business Acquisition [Line Items]
Cash purchase price		$ 443
Identifiable assets acquired:
Investments		770
Cash		8
Premiums receivable, net of commissions payable, fair value of net assets acquired, before settlement of pre-existing relationships		18
Ceded unearned premium reserve, fair value of net assets acquired, before settlement of pre-existing relationships		173
Ceded unearned premium reserve, net effect of settlement of pre-existing relationships		(173)
Deferred acquisition costs, fair value of net assets acquired, before settlement of pre-existing relationships		1
Deferred acquisition costs, net effect of settlement of pre-existing relationships		(1)
Salvage and subrogation recoverable		23
Credit derivative assets		1
Deferred tax assets, net, fair value of net assets acquired, before settlement of pre-existing relationships		194
Deferred tax asset, net effect of settlement of pre-exiting relationships		34
Deferred tax asset, net effect of CIFG acquisition		228
Other assets, fair value of net assets acquired, before settlement of pre-existing relationships		4
Total assets, fair value of net assets acquired, before settlement of pre-existing relationships		1,192
Total assets, net of settlement of pre-existing relationships		(140)
Total assets, Net effect of MBIA UK Acquisition		1,052
Liabilities assumed:
Unearned premium reserves, fair value of net assets acquired, before settlement of pre-existing relationships		306
Unearned premium reserves, net of settlement of pre-existing relationships		(10)
Unearned premium reserves, Net effect of MBIA UK Acquisition		296
Loss and loss adjustments expense reserve, fair value of net assets acquired before settlements of pre-existing relationships		1
Loss and loss adjustments expense reserve, net effect of settlement of pre-existing relationships		(66)
Loss and loss adjustments expense reserve, net effect of CIFG acquisition		(65)
Credit derivative liabilities, fair value of net assets acquired before settlement of pre-existing relationships		68
Other liabilities, fair value of net assets acquired, before settlement of pre-existing relationships		17
Total liabilities, fair value of net assets acquired, before settlement of pre-existing relationships		392
Total liabilities, net of settlement of pre-existing relationships		(76)
Total liabilities, Net effect of MBIA UK Acquisition		316
Net assets effect of MBIA UK Acquisition, fair value of net assets acquired, before settlement of pre-existing relationships		800
Net assets effect of MBIA UK Acquisition, net of settlement of pre-existing relationships		(64)
Net asset effect of MBIA UK Acquisition, Net effect of MBIA UK Acquisition		736
Bargain purchase gain and settlement of pre-existing relationships resulting from MBIA UK Acquisition, after tax, fair value of net assets acquired, before settlement of pre-existing relationships		357
Bargain purchase gain and settlement of pre-existing relationships resulting from MBIA UK Acquisition, after-tax, net of settlement of pre-existing relationships		(64)
Bargain purchase gain and settlement of pre-existing relationships resulting from MBIA UK Acquisition, after-tax, Net effect of MBIA UK Acquisition		293
Deferred tax, net of settlement of pre-existing relationships		(34)
Deferred tax, Net effect of MBIA UK Acquisition		(34)
Bargain purchase gain and settlement of pre-existing relationships resulting from MBIA UK Acquisitions, pre-tax, fair value of net assets acquired, before settlement of pre-existing relationships		357
Bargain purchase gain and settlement of pre-existing relationships resulting from MBIA UK Acquisition, pre-tax, net of settlement of pre-existing relationships		(98)
Bargain purchase gain and settlement of pre-existing relationships resulting from MBIA UK Acquisition, pre-tax, Net effect of MBIA UK Acquisition		259
Assumed assets including pre-existing relationship		627
Settlement of pre-existing relationship		(173)
Consideration transferred		$ 270
MBIA UK [Member]
Business Acquisition [Line Items]
Cash purchase price	$ 334
Identifiable assets acquired:
Investments	459
Cash	72
Premiums receivable, net of commissions payable, fair value of net assets acquired, before settlement of pre-existing relationships	274
Premiums receivable, net of commissions payable, net of settlement of pre-existing relationships	(4)
Premiums receivable, net of commissions payable, net effect of MBIA UK Acquisition	270
Other assets, fair value of net assets acquired, before settlement of pre-existing relationships	16
Other assets, net of settlement of pre-existing relationships	(6)
Other assets, Net effect of MBIA UK Acquisition	10
Total assets, fair value of net assets acquired, before settlement of pre-existing relationships	821
Total assets, net of settlement of pre-existing relationships	(10)
Total assets, Net effect of MBIA UK Acquisition	811
Liabilities assumed:
Unearned premium reserves, fair value of net assets acquired, before settlement of pre-existing relationships	389
Unearned premium reserves, net of settlement of pre-existing relationships	(6)
Unearned premium reserves, Net effect of MBIA UK Acquisition	383
Current tax payable, fair value of net assets acquired, before settlement of pre-existing relationships	25
Current tax payable, net of settlement of pre-existing relationships	0
Current tax payable, Net effect of MBIA UK Acquisition	25
Other liabilities, fair value of net assets acquired, before settlement of pre-existing relationships	4
Other liabilities, net of settlement of pre-existing relationships	(5)
Other liabilities, Net effect of MBIA UK Acquisition	(1)
Total liabilities, fair value of net assets acquired, before settlement of pre-existing relationships	418
Total liabilities, net of settlement of pre-existing relationships	(11)
Total liabilities, Net effect of MBIA UK Acquisition	407
Net assets of MBIA UK, fair value of net assets acquired, before settlement of pre-existing relationships	403
Net assets of MBIA UK, net of settlement of pre-existing relationships	1
Net assets of MBIA UK, Net effect of MBIA UK Acquisition	404
Cash acquired from MBIA Holdings, fair value of net assets acquired, before settlement of pre-existing relationships	23
Cash acquired from MBIA Holdings, net of settlement of pre-existing relationships	0
Cash acquired from MBIA Holdings, Net effect of MBIA UK Acquisition	23
Deferred tax liability, fair value of net assets acquired, before settlement of pre-existing relationships	(36)
Deferred tax liability, net of settlement of pre-existing relationships	0
Deferred tax liability, Net effect of MBIA UK Acquisition	(36)
Net assets effect of MBIA UK Acquisition, fair value of net assets acquired, before settlement of pre-existing relationships	390
Net assets effect of MBIA UK Acquisition, net of settlement of pre-existing relationships	1
Net asset effect of MBIA UK Acquisition, Net effect of MBIA UK Acquisition	391
Bargain purchase gain and settlement of pre-existing relationships resulting from MBIA UK Acquisition, after tax, fair value of net assets acquired, before settlement of pre-existing relationships	56
Bargain purchase gain and settlement of pre-existing relationships resulting from MBIA UK Acquisition, after-tax, net of settlement of pre-existing relationships	1
Bargain purchase gain and settlement of pre-existing relationships resulting from MBIA UK Acquisition, after-tax, Net effect of MBIA UK Acquisition	57
Deferred tax, net of settlement of pre-existing relationships	1
Deferred tax, Net effect of MBIA UK Acquisition	1
Bargain purchase gain and settlement of pre-existing relationships resulting from MBIA UK Acquisitions, pre-tax, fair value of net assets acquired, before settlement of pre-existing relationships	56
Bargain purchase gain and settlement of pre-existing relationships resulting from MBIA UK Acquisition, pre-tax, net of settlement of pre-existing relationships	2
Bargain purchase gain and settlement of pre-existing relationships resulting from MBIA UK Acquisition, pre-tax, Net effect of MBIA UK Acquisition	58
Assumed assets including pre-existing relationship	385
Settlement of pre-existing relationship	5
Consideration transferred	$ 329