CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (Parenthetical) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Statement of Partners' Capital [Abstract]
Tax benefit of change in postretirement benefit plans	$ (38.8)		$ 399.0
Tax expense of net change in unrealized gains on investment securities		1.0	7.8
Tax benefit of amortization of prior service costs	(0.1)		(1.0)
Tax benefit of amortization of net actuarial loss	(4.8)		(42.1)
Tax (expense) benefit of prior service gain from plan amendment	(7.1)		(1.0)
Tax benefit (expense) of net actuarial gain (loss) arising during the period	(26.8)		443.1
Tax expense of gains realized during the period		1.0	6.1
Tax benefit (expense) of Unrealized holding (losses) gains arising during period			$ 1.7