Related Party Transactions (Payables To Related Parties) (Detail) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Related Party Transaction [Line Items]
Payables to related parties	$ 42	$ 18
Explorer
Related Party Transaction [Line Items]
Payables to related parties	1	3
Illinois Extension Pipeline
Related Party Transaction [Line Items]
Payables to related parties	4	0
LOCAP
Related Party Transaction [Line Items]
Payables to related parties	2	2
LOOP
Related Party Transaction [Line Items]
Payables to related parties	5	4
MarkWest Utica EMG
Related Party Transaction [Line Items]
Payables to related parties	19	0
Ohio Condensate
Related Party Transaction [Line Items]
Payables to related parties	4	0
TAAE
Related Party Transaction [Line Items]
Payables to related parties	1	2
TACE
Related Party Transaction [Line Items]
Payables to related parties	2	2
TAME
Related Party Transaction [Line Items]
Payables to related parties	3	5
Other equity method investees
Related Party Transaction [Line Items]
Payables to related parties	$ 1	$ 0