Employee and Agent Benefits (Details 3) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Pension benefits
Defined benefit plan, fair value of plan assets
Fair value of plan assets	$ 1,925.6	$ 1,682.1	$ 1,429.0
Qualified defined benefit pension plans
Defined benefit plan, fair value of plan assets
Fair value of plan assets	1,925.6	1,682.1
Qualified defined benefit pension plans \| U.S. large cap equity portfolios
Defined benefit plan, fair value of plan assets
Fair value of plan assets	414.0	601.8
Qualified defined benefit pension plans \| U.S. small/mid cap equity portfolios
Defined benefit plan, fair value of plan assets
Fair value of plan assets	102.9	156.2
Qualified defined benefit pension plans \| Balance asset allocation portfolios
Defined benefit plan, fair value of plan assets
Fair value of plan assets	96.9	82.4
Qualified defined benefit pension plans \| International equity portfolios
Defined benefit plan, fair value of plan assets
Fair value of plan assets	171.0	273.9
Qualified defined benefit pension plans \| Fixed income security portfolios
Defined benefit plan, fair value of plan assets
Fair value of plan assets	1,048.5	486.6
Qualified defined benefit pension plans \| Direct real estate investments
Defined benefit plan, fair value of plan assets
Fair value of plan assets	92.3	81.2
Qualified defined benefit pension plans \| Fair value hierarchy Level 2
Defined benefit plan, fair value of plan assets
Fair value of plan assets	1,925.6	1,682.1
Qualified defined benefit pension plans \| Fair value hierarchy Level 2 \| U.S. large cap equity portfolios
Defined benefit plan, fair value of plan assets
Fair value of plan assets	414.0	601.8
Qualified defined benefit pension plans \| Fair value hierarchy Level 2 \| U.S. small/mid cap equity portfolios
Defined benefit plan, fair value of plan assets
Fair value of plan assets	102.9	156.2
Qualified defined benefit pension plans \| Fair value hierarchy Level 2 \| Balance asset allocation portfolios
Defined benefit plan, fair value of plan assets
Fair value of plan assets	96.9	82.4
Qualified defined benefit pension plans \| Fair value hierarchy Level 2 \| International equity portfolios
Defined benefit plan, fair value of plan assets
Fair value of plan assets	171.0	273.9
Qualified defined benefit pension plans \| Fair value hierarchy Level 2 \| Fixed income security portfolios
Defined benefit plan, fair value of plan assets
Fair value of plan assets	1,048.5	486.6
Qualified defined benefit pension plans \| Fair value hierarchy Level 2 \| Direct real estate investments
Defined benefit plan, fair value of plan assets
Fair value of plan assets	92.3	81.2
Qualified defined benefit pension plans \| Fair value hierarchy Level 3 \| Direct real estate investments
Defined benefit plan, fair value of plan assets
Fair value of plan assets				84.7
Other postretirement benefits
Defined benefit plan, fair value of plan assets
Fair value of plan assets	613.0	519.7	466.6
Fair value of plan assets included in trust owned life insurance contract	77.7	59.4
Other postretirement benefits \| Cash and cash equivalents
Defined benefit plan, fair value of plan assets
Fair value of plan assets	4.7	1.9
Other postretirement benefits \| U.S. equity portfolios
Defined benefit plan, fair value of plan assets
Fair value of plan assets	351.6	260.8
Other postretirement benefits \| International equity portfolios
Defined benefit plan, fair value of plan assets
Fair value of plan assets	60.0	51.4
Other postretirement benefits \| Fixed income investment funds
Defined benefit plan, fair value of plan assets
Fair value of plan assets	157.9	163.5
Other postretirement benefits \| Principal Life general account investment
Defined benefit plan, fair value of plan assets
Fair value of plan assets	38.8	42.1
Other postretirement benefits \| Fair value hierarchy Level 1
Defined benefit plan, fair value of plan assets
Fair value of plan assets	496.5	418.2
Other postretirement benefits \| Fair value hierarchy Level 1 \| Cash and cash equivalents
Defined benefit plan, fair value of plan assets
Fair value of plan assets	4.7	1.9
Other postretirement benefits \| Fair value hierarchy Level 1 \| U.S. equity portfolios
Defined benefit plan, fair value of plan assets
Fair value of plan assets	288.0	213.5
Other postretirement benefits \| Fair value hierarchy Level 1 \| International equity portfolios
Defined benefit plan, fair value of plan assets
Fair value of plan assets	45.9	39.3
Other postretirement benefits \| Fair value hierarchy Level 1 \| Fixed income investment funds
Defined benefit plan, fair value of plan assets
Fair value of plan assets	157.9	163.5
Other postretirement benefits \| Fair value hierarchy Level 2
Defined benefit plan, fair value of plan assets
Fair value of plan assets	77.7	59.4
Other postretirement benefits \| Fair value hierarchy Level 2 \| U.S. equity portfolios
Defined benefit plan, fair value of plan assets
Fair value of plan assets	63.6	47.3
Other postretirement benefits \| Fair value hierarchy Level 2 \| International equity portfolios
Defined benefit plan, fair value of plan assets
Fair value of plan assets	14.1	12.1
Other postretirement benefits \| Fair value hierarchy Level 3
Defined benefit plan, fair value of plan assets
Fair value of plan assets	38.8	42.1
Other postretirement benefits \| Fair value hierarchy Level 3 \| Principal Life general account investment
Defined benefit plan, fair value of plan assets
Fair value of plan assets	$ 38.8	$ 42.1	$ 42.5	$ 44.5

Assets, usually stocks, bonds, and other investments, that have been segregated and restricted (usually in a trust) to provide benefits, at their fair value as of the measurement date. Plan assets include amounts contributed by the employer (and by employees for a contributory plan) and amounts earned from investing the contributions, less benefits paid. If a plan has liabilities other than for benefits, those non-benefit obligations may be considered as reductions of plan assets.

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