Paid Claims Development, Net of Reinsurance (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Claims Development [Line Items]
Liability for policy and contract claims		$ 10,958	$ 10,295
U.S. Mortgage Insurance
Claims Development [Line Items]
Total incurred	[1]	4,025
Total paid	[1]	3,805
All outstanding liabilities before 2010		13
Liability for policy and contract claims		233
U.S. Mortgage Insurance | Accident Year 2010
Claims Development [Line Items]
Total incurred	[1]	1,174	1,174	$ 1,174	$ 1,173	$ 1,173	$ 1,165	$ 1,146	$ 1,139	$ 1,157	$ 977
Total paid	[1]	1,170	1,167	1,158	1,139	1,109	1,049	973	844	567	140
U.S. Mortgage Insurance | Accident Year 2011
Claims Development [Line Items]
Total incurred	[1]	938	939	939	939	938	929	913	931	910
Total paid	[1]	937	935	927	906	874	816	722	497	65
U.S. Mortgage Insurance | Accident Year 2012
Claims Development [Line Items]
Total incurred	[1]	666	667	668	671	673	671	675	718
Total paid	[1]	662	658	650	634	602	532	391	92
U.S. Mortgage Insurance | Accident Year 2013
Claims Development [Line Items]
Total incurred	[1]	381	382	384	387	392	407	475
Total paid	[1]	375	372	362	340	297	202	44
U.S. Mortgage Insurance | Accident Year 2014
Claims Development [Line Items]
Total incurred	[1]	258	259	261	269	288	328
Total paid	[1]	253	247	233	195	127	22
U.S. Mortgage Insurance | Accident Year 2015
Claims Development [Line Items]
Total incurred	[1]	180	181	187	208	235
Total paid	[1]	173	167	145	85	12
U.S. Mortgage Insurance | Accident Year 2016
Claims Development [Line Items]
Total incurred	[1]	136	138	160	198
Total paid	[1]	124	110	64	10
U.S. Mortgage Insurance | Accident Year 2017
Claims Development [Line Items]
Total incurred	[1]	102	121	171
Total paid	[1]	77	46	6
U.S. Mortgage Insurance | Accident Year 2018
Claims Development [Line Items]
Total incurred	[1]	84	117
Total paid	[1]	32	3
U.S. Mortgage Insurance | Accident Year 2019
Claims Development [Line Items]
Total incurred	[1]	106
Total paid	[1]	2
Australia Mortgage Insurance
Claims Development [Line Items]
Total incurred	[1],[2]	982
Total paid	[1],[2]	775
Other	[2],[3]	1
All outstanding liabilities before 2010		0
Liability for policy and contract claims		208
Australia Mortgage Insurance | Accident Year 2010
Claims Development [Line Items]
Total incurred	[1],[2]	128	128	129	128	130	130	132	132	101	52
Total paid	[1],[2]	128	128	128	128	128	126	124	104	29	$ 6
Australia Mortgage Insurance | Accident Year 2011
Claims Development [Line Items]
Total incurred	[1],[2]	122	122	123	123	125	127	132	136	71
Total paid	[1],[2]	122	122	122	122	122	120	112	69	$ 4
Australia Mortgage Insurance | Accident Year 2012
Claims Development [Line Items]
Total incurred	[1],[2]	87	87	87	87	91	94	107	67
Total paid	[1],[2]	87	87	86	85	84	80	62	$ 11
Australia Mortgage Insurance | Accident Year 2013
Claims Development [Line Items]
Total incurred	[1],[2]	62	62	61	65	71	83	63
Total paid	[1],[2]	61	61	60	58	52	36	$ 10
Australia Mortgage Insurance | Accident Year 2014
Claims Development [Line Items]
Total incurred	[1],[2]	64	64	66	71	84	60
Total paid	[1],[2]	63	62	59	47	26	$ 6
Australia Mortgage Insurance | Accident Year 2015
Claims Development [Line Items]
Total incurred	[1],[2]	84	86	89	106	71
Total paid	[1],[2]	80	77	66	28	$ 4
Australia Mortgage Insurance | Accident Year 2016
Claims Development [Line Items]
Total incurred	[1],[2]	110	116	130	97
Total paid	[1],[2]	96	86	52	$ 6
Australia Mortgage Insurance | Accident Year 2017
Claims Development [Line Items]
Total incurred	[1],[2]	108	125	92
Total paid	[1],[2]	77	50	$ 9
Australia Mortgage Insurance | Accident Year 2018
Claims Development [Line Items]
Total incurred	[1],[2]	109	88
Total paid	[1],[2]	47	$ 11
Australia Mortgage Insurance | Accident Year 2019
Claims Development [Line Items]
Total incurred	[1],[2]	108
Total paid	[1],[2]	$ 14

[1] Represents the year in which first monthly mortgage payments have been missed by the borrower.

[2] Amounts translated into U.S. dollars at the average foreign exchange rates for the year ended December 31, 2019.

[3] Includes foreign currency translation.