Benefit Plans (Investment Allocation Strategy) (Details) - Return Seeking Investments	12 Months Ended
	Dec. 31, 2015
≤97%
Minimum	36.00%
Target	40.00%
Maximum	44.00%
98%
Minimum	34.00%
Target	38.00%
Maximum	42.00%
99%
Minimum	31.00%
Target	35.00%
Maximum	39.00%
100%
Minimum	30.00%
Target	33.00%
Maximum	36.00%
101%
Minimum	28.00%
Target	31.00%
Maximum	34.00%
102%
Minimum	26.00%
Target	29.00%
Maximum	32.00%
103%
Minimum	23.00%
Target	26.00%
Maximum	29.00%
104%
Minimum	21.00%
Target	24.00%
Maximum	27.00%
105%
Minimum	18.00%
Target	21.00%
Maximum	24.00%
106%
Minimum	16.00%
Target	18.00%
Maximum	20.00%
107%
Minimum	12.00%
Target	14.00%
Maximum	16.00%
≥108%
Minimum	8.00%
Target	10.00%
Maximum	12.00%