Acquisitions - Assets and Liabilities Assumed (Details) - USD ($) $ in Millions	Jul. 01, 2016	Apr. 01, 2015
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	18
Ceded unearned premium reserve before settlement of pre-existing relationships	173
Ceded unearned premium reserve, net effect of settlement of pre-existing relationships	(173)
Deferred acquisition costs 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 asset, net before settlement of pre-existing relationships	194
Deferred tax asset, net, settlement of pre-existing relationships	34
Deferred tax asset, net	228
Other assets before settlement of pre-existing relationships	4
Total assets before settlement of pre-existing relationships	1,192
Total assets, net effect of settlement of pre-existing relationships	(140)
Total assets	1,052
Liabilities assumed:
Unearned premium reserves before settlement of pre-existing relationships	306
Unearned premium reserves, net effect of settlement of pre-existing relationships	(10)
Unearned premium reserves	296
Loss and loss adjustment expense reserve before settlement of pre-existing relationships	1
Loss and loss adjustment expense reserve, net effect of settlement of pre-existing relationships	(66)
Loss and loss adjustment expense reserve	(65)
Credit derivative liabilities before settlement of pre-existing relationships	68
Other liabilities before settlement of pre-existing relationships	17
Total liabilities before settlement of pre-existing relationships	392
Total liabilities, net effect of settlement of pre-existing relationships	(76)
Total liabilities	316
Net asset effect of acquisition before settlement of pre-existing relationships	800
Net asset effect of acquisition, net effect of settlement of pre-existing relationships	(64)
Net asset effect of acquisition	736
Bargain purchase gain and settlement of pre-existing relationships resulting from acquisition before settlement of pre-existing relationships	357
Bargain purchase gain and settlement of pre-existing relationships resulting from acquisitions, net effect of settlement of pre-existing relationships	(64)
Bargain purchase gain and settlement of pre-existing relationships resulting from acquisitions	293
Deferred tax, net effect of settlement of pre-existing relationships	(34)
Deferred tax	(34)
Bargain purchase gain and settlement of pre-existing relationships resulting from acquisition before settlement of pre-existing relationships	357
Bargain purchase gain and settlement of pre-existing relationship resulting from acquisition, pre-tax, net effect of settlement of pre-existing relationships	(98)
Bargain purchase gain and settlement of pre-existing relationships resulting from acquisition, pre-tax	259
Consideration transferred	270
Assumed assets including pre-existing relationship	627
Settlement of pre-existing relationship	$ 173
Radian [Member]
Business Acquisition [Line Items]
Cash purchase price		$ 804
Identifiable assets acquired:
Investments		1,473
Cash		4
Ceded unearned premium reserve before settlement of pre-existing relationships		(3)
Ceded unearned premium reserve, net effect of settlement of pre-existing relationships		(65)
Ceded unearned premium reserve		(68)
Credit derivative assets		30
Deferred tax asset, net before settlement of pre-existing relationships		263
Deferred tax asset, net, settlement of pre-existing relationships		(56)
Deferred tax asset, net		207
Financial guaranty variable interest entities’ assets		122
Other assets before settlement of pre-existing relationships		86
Other assets, settlement of pre-existing relationship		(67)
Other assets		19
Total assets before settlement of pre-existing relationships		1,975
Total assets, net effect of settlement of pre-existing relationships		(188)
Total assets		1,787
Liabilities assumed:
Unearned premium reserves before settlement of pre-existing relationships		697
Unearned premium reserves, net effect of settlement of pre-existing relationships		(216)
Unearned premium reserves		481
Credit derivative liabilities before settlement of pre-existing relationships		271
Credit derivative liabilities, net effect of settlement of pre-existing relationships		(26)
Credit derivative liabilities		245
Financial guaranty variable interest entities’ liabilities		118
Other liabilities before settlement of pre-existing relationships		30
Other liabilities, net effect of settlement of pre-existing relationships		(49)
Other liabilities		(19)
Total liabilities before settlement of pre-existing relationships		1,116
Total liabilities, net effect of settlement of pre-existing relationships		(291)
Total liabilities		825
Net asset effect of acquisition before settlement of pre-existing relationships		859
Net asset effect of acquisition, net effect of settlement of pre-existing relationships		103
Net asset effect of acquisition		962
Bargain purchase gain and settlement of pre-existing relationships resulting from acquisition before settlement of pre-existing relationships		55
Bargain purchase gain and settlement of pre-existing relationships resulting from acquisitions, net effect of settlement of pre-existing relationships		103
Bargain purchase gain and settlement of pre-existing relationships resulting from acquisitions		158
Deferred tax, net effect of settlement of pre-existing relationships		56
Deferred tax		56
Bargain purchase gain and settlement of pre-existing relationships resulting from acquisition before settlement of pre-existing relationships		55
Bargain purchase gain and settlement of pre-existing relationship resulting from acquisition, pre-tax, net effect of settlement of pre-existing relationships		159
Bargain purchase gain and settlement of pre-existing relationships resulting from acquisition, pre-tax		214
Consideration transferred		987
Assumed assets including pre-existing relationship		1,042
Settlement of pre-existing relationship		$ 183