Significant Accounting Policies - Effects of Revision on PHI's Consolidated Balance Sheets (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Deferred income tax liabilities, net		$ 2,717	$ 3,208	$ 2,895
Total deferred credits		4,302	4,851	4,565
Retained earnings	555	580	1,077	1,040	1,027	1,236
Total equity	4,236	4,246	4,414	4,304
As Filed [Member]
Deferred income tax liabilities, net		2,685	3,176	2,863
Total deferred credits		4,270	4,819	4,533
Retained earnings		612	1,109	1,072	1,059	1,268
Total equity		4,278	4,446	4,336
Adjustment [Member]
Deferred income tax liabilities, net	32	32	32	32
Total deferred credits		32	32	32
Retained earnings		(32)	(32)	(32)	(32)	(32)
Total equity		$ (32)	$ (32)	$ (32)