Debt (Narrative) (Details) - USD ($)	3 Months Ended
	Mar. 31, 2016	Mar. 01, 2016	Dec. 31, 2015
Floating-rate debt outstanding	$ 1,302,900,000		$ 1,331,700,000
Note Payable To Phillips 66, Due 2020, 3.0 percent [Member] | Phillips 66 [Member]
Interest rate, stated percentage	3.00%	3.00%
Penalty for payment of note in whole or in part prior to maturity	$ 0
Fixed Rate Debt [Member] | Fair Value, Inputs, Level 2 [Member]
Aggregate fair value of fixed-rate debt	1,215,800,000
Floating Rate Debt [Member]
Floating-rate debt outstanding	$ 0		$ 0