Outstanding Exposure - Financial Guaranty Portfolio by Asset Class (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013
Schedule of Insured Financial Obligations [Line Items]
Gross par outstanding	$ 426,704		$ 487,895
Ceded Par Amount	22,975	[1]	28,788
Net Par Outstanding (excluding loss mitigation bonds)	403,729	[2]	459,107	[3]
Public Finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Gross par outstanding	373,360		409,890
Ceded Par Amount	19,878		23,711
Net Par Outstanding (excluding loss mitigation bonds)	353,482		386,179
Structured Finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Gross par outstanding	53,344		78,005
Ceded Par Amount	3,097		5,077
Net Par Outstanding (excluding loss mitigation bonds)	50,247		72,928
United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding (excluding loss mitigation bonds)	363,294
United States [Member] | Public Finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Gross par outstanding	334,906		367,616
Ceded Par Amount	12,783		15,435
Net Par Outstanding (excluding loss mitigation bonds)	322,123	[2]	352,181	[3]
United States [Member] | Public Finance [Member] | General obligation [Member]
Schedule of Insured Financial Obligations [Line Items]
Gross par outstanding	144,714		160,751
Ceded Par Amount	4,438		5,474
Net Par Outstanding (excluding loss mitigation bonds)	140,276		155,277
United States [Member] | Public Finance [Member] | Tax backed [Member]
Schedule of Insured Financial Obligations [Line Items]
Gross par outstanding	65,600		70,552
Ceded Par Amount	3,075		3,728
Net Par Outstanding (excluding loss mitigation bonds)	62,525		66,824
United States [Member] | Public Finance [Member] | Municipal utilities [Member]
Schedule of Insured Financial Obligations [Line Items]
Gross par outstanding	53,471		57,893
Ceded Par Amount	1,381		1,569
Net Par Outstanding (excluding loss mitigation bonds)	52,090		56,324
United States [Member] | Public Finance [Member] | Transportation [Member]
Schedule of Insured Financial Obligations [Line Items]
Gross par outstanding	28,914		32,514
Ceded Par Amount	1,091		1,684
Net Par Outstanding (excluding loss mitigation bonds)	27,823		30,830
United States [Member] | Public Finance [Member] | Healthcare [Member]
Schedule of Insured Financial Obligations [Line Items]
Gross par outstanding	16,225		17,663
Ceded Par Amount	1,377		1,531
Net Par Outstanding (excluding loss mitigation bonds)	14,848		16,132
United States [Member] | Public Finance [Member] | Higher education [Member]
Schedule of Insured Financial Obligations [Line Items]
Gross par outstanding	13,485		14,470
Ceded Par Amount	386		399
Net Par Outstanding (excluding loss mitigation bonds)	13,099		14,071
United States [Member] | Public Finance [Member] | Infrastructure finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Gross par outstanding	5,098		5,014
Ceded Par Amount	917		900
Net Par Outstanding (excluding loss mitigation bonds)	4,181		4,114
United States [Member] | Public Finance [Member] | Housing [Member]
Schedule of Insured Financial Obligations [Line Items]
Gross par outstanding	2,880		3,518
Ceded Par Amount	101		132
Net Par Outstanding (excluding loss mitigation bonds)	2,779		3,386
United States [Member] | Public Finance [Member] | Investor-owned utilities [Member]
Schedule of Insured Financial Obligations [Line Items]
Gross par outstanding	944		992
Ceded Par Amount	0		1
Net Par Outstanding (excluding loss mitigation bonds)	944		991
United States [Member] | Public Finance [Member] | Other public/structured finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Gross par outstanding	3,575		4,249
Ceded Par Amount	17		17
Net Par Outstanding (excluding loss mitigation bonds)	3,558		4,232
United States [Member] | Structured Finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Gross par outstanding	43,288		62,591
Ceded Par Amount	2,117		3,684
Net Par Outstanding (excluding loss mitigation bonds)	41,171	[2]	58,907	[3]
United States [Member] | Structured Finance [Member] | Other public/structured finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Gross par outstanding	858		2,067
Ceded Par Amount	144		1,080
Net Par Outstanding (excluding loss mitigation bonds)	714		987
United States [Member] | Structured Finance [Member] | Pooled corporate obligations [Member]
Schedule of Insured Financial Obligations [Line Items]
Gross par outstanding	21,791		32,955
Ceded Par Amount	1,145		1,630
Net Par Outstanding (excluding loss mitigation bonds)	20,646		31,325
United States [Member] | Structured Finance [Member] | RMBS [Member]
Schedule of Insured Financial Obligations [Line Items]
Gross par outstanding	10,109		14,542
Ceded Par Amount	692		821
Net Par Outstanding (excluding loss mitigation bonds)	9,417		13,721
United States [Member] | Structured Finance [Member] | Commercial mortgage-backed securities (CMBS) and other commercial real estate related exposures [Member]
Schedule of Insured Financial Obligations [Line Items]
Gross par outstanding	1,979		3,990
Ceded Par Amount	22		38
Net Par Outstanding (excluding loss mitigation bonds)	1,957		3,952
United States [Member] | Structured Finance [Member] | Insurance securitizations [Member]
Schedule of Insured Financial Obligations [Line Items]
Gross par outstanding	3,480		3,082
Ceded Par Amount	47		47
Net Par Outstanding (excluding loss mitigation bonds)	3,433		3,035
United States [Member] | Structured Finance [Member] | Financial product [Member]
Schedule of Insured Financial Obligations [Line Items]
Gross par outstanding	2,276		2,709
Ceded Par Amount	0		0
Net Par Outstanding (excluding loss mitigation bonds)	2,276		2,709
United States [Member] | Structured Finance [Member] | Consumer receivables [Member]
Schedule of Insured Financial Obligations [Line Items]
Gross par outstanding	2,157		2,257
Ceded Par Amount	58		59
Net Par Outstanding (excluding loss mitigation bonds)	2,099		2,198
United States [Member] | Structured Finance [Member] | Commercial receivables [Member]
Schedule of Insured Financial Obligations [Line Items]
Gross par outstanding	567		918
Ceded Par Amount	7		7
Net Par Outstanding (excluding loss mitigation bonds)	560		911
United States [Member] | Structured Finance [Member] | Structured credit [Member]
Schedule of Insured Financial Obligations [Line Items]
Gross par outstanding	71		71
Ceded Par Amount	2		2
Net Par Outstanding (excluding loss mitigation bonds)	69		69
Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding (excluding loss mitigation bonds)	40,435
Non United States [Member] | Public Finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Gross par outstanding	38,454		42,274
Ceded Par Amount	7,095		8,276
Net Par Outstanding (excluding loss mitigation bonds)	31,359	[2]	33,998	[3]
Non United States [Member] | Public Finance [Member] | Infrastructure finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Gross par outstanding	15,091		17,373
Ceded Par Amount	2,283		2,670
Net Par Outstanding (excluding loss mitigation bonds)	12,808		14,703
Non United States [Member] | Public Finance [Member] | Regulated utilities [Member]
Schedule of Insured Financial Obligations [Line Items]
Gross par outstanding	14,582		15,502
Ceded Par Amount	3,668		4,297
Net Par Outstanding (excluding loss mitigation bonds)	10,914		11,205
Non United States [Member] | Public Finance [Member] | Pooled infrastructure [Member]
Schedule of Insured Financial Obligations [Line Items]
Gross par outstanding	2,565		2,754
Ceded Par Amount	145		234
Net Par Outstanding (excluding loss mitigation bonds)	2,420		2,520
Non United States [Member] | Public Finance [Member] | Other public/structured finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Gross par outstanding	6,216		6,645
Ceded Par Amount	999		1,075
Net Par Outstanding (excluding loss mitigation bonds)	5,217		5,570
Non United States [Member] | Structured Finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Gross par outstanding	10,056		15,414
Ceded Par Amount	980		1,393
Net Par Outstanding (excluding loss mitigation bonds)	9,076	[2]	14,021	[3]
Non United States [Member] | Structured Finance [Member] | Other public/structured finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Gross par outstanding	750		403
Ceded Par Amount	25		25
Net Par Outstanding (excluding loss mitigation bonds)	725		378
Non United States [Member] | Structured Finance [Member] | Pooled corporate obligations [Member]
Schedule of Insured Financial Obligations [Line Items]
Gross par outstanding	7,439		12,232
Ceded Par Amount	835		1,174
Net Par Outstanding (excluding loss mitigation bonds)	6,604		11,058
Non United States [Member] | Structured Finance [Member] | RMBS [Member]
Schedule of Insured Financial Obligations [Line Items]
Gross par outstanding	893		1,296
Ceded Par Amount	99		150
Net Par Outstanding (excluding loss mitigation bonds)	794		1,146
Non United States [Member] | Structured Finance [Member] | Commercial receivables [Member]
Schedule of Insured Financial Obligations [Line Items]
Gross par outstanding	965		1,286
Ceded Par Amount	21		23
Net Par Outstanding (excluding loss mitigation bonds)	944		1,263
Non United States [Member] | Structured Finance [Member] | Structured credit [Member]
Schedule of Insured Financial Obligations [Line Items]
Gross par outstanding	9		197
Ceded Par Amount	0		21
Net Par Outstanding (excluding loss mitigation bonds)	$ 9		$ 176

[1] Includes par related to insured credit derivatives.

[2] Excludes $1.3 billion of loss mitigation securities insured and held by the Company as of December 31, 2014, which are primarily in the BIG category.

[3] Excludes $1.2 billion of loss mitigation securities insured and held by the Company as of December 31, 2013, which are primarily in the BIG category.