Consolidated Statements of Cash Flows - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating activities
Net income (loss)	$ 2,324.5	$ 1,361.8	$ 1,253.2
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Net realized capital (gains) losses	(524.2)	(171.1)	51.1
Depreciation and amortization expense	195.7	186.6	193.0
Amortization of deferred acquisition costs	234.6	285.1	270.8
Additions to deferred acquisition costs	(421.8)	(402.3)	(390.3)
Stock-based compensation	82.7	84.4	84.5
(Income) loss from equity method investments, net of dividends received	(68.2)	(0.6)	97.8
Changes in:
Accrued investment income	(30.0)	(35.0)	(39.7)
Net cash flows for trading securities	(332.2)	166.5	(201.9)
Premiums due and other receivables	(114.2)	98.7	(211.5)
Contractholder and policyholder liabilities and dividends	3,296.8	2,140.3	3,283.6
Current and deferred income taxes (benefits)	(164.4)	45.8	(66.5)
Real estate acquired through operating activities	(82.6)	(58.2)	(44.1)
Real estate sold through operating activities	1.4	229.0	53.7
Other assets and liabilities	(227.1)	(1.1)	145.7
Other	17.0	(72.1)	(102.3)
Net adjustments	1,863.5	2,496.0	3,123.9
Net cash provided by (used in) operating activities	4,188.0	3,857.8	4,377.1
Investing activities
Available-for-sale securities: Purchases	(13,371.6)	(13,763.8)	(9,920.3)
Available-for-sale securities: Sales	1,413.6	1,890.5	1,563.0
Available-for-sale securities: Maturities	8,743.2	7,742.8	6,625.9
Mortgage loans acquired or originated	(2,755.8)	(2,889.0)	(2,275.1)
Mortgage loans sold or repaid	1,872.0	2,068.7	1,687.3
Real estate acquired	(200.5)	(109.7)	(322.0)
Real estate sold	481.9	35.5	208.9
Net (purchases) sales of property and equipment	(164.8)	(154.9)	(136.4)
Purchase of interests in subsidiaries, net of cash acquired			(291.2)
Net change in other investments	(70.8)	26.0	(307.7)
Net cash provided by (used in) investing activities	(4,052.8)	(5,153.9)	(3,167.6)
Financing activities
Issuance of common stock	162.5	37.8	76.1
Acquisition of treasury stock	(220.4)	(277.3)	(300.6)
Proceeds from financing element derivatives	0.1	0.4	0.3
Payments for financing element derivatives	(77.6)	(87.7)	(82.0)
Excess tax benefits from share-based payment arrangements		12.0	15.7
Purchase of subsidiary shares from noncontrolling interest	(13.3)	(2.4)	(22.5)
Dividends to common stockholders	(540.0)	(464.9)	(441.0)
Dividends to preferred stockholders			(16.5)
Preferred stock redemption			(550.0)
Issuance of long-term debt	2.8	656.1	804.9
Principal repayments of long-term debt	(56.5)	(799.3)	(52.6)
Net proceeds from (repayments of) short-term borrowings	(15.5)	(131.4)	157.0
Investment contract deposits	10,154.4	10,770.9	6,492.3
Investment contract withdrawals	(9,914.6)	(8,392.7)	(6,666.8)
Net increase (decrease) in banking operation deposits	136.6	129.0	91.1
Other	(2.5)	0.4	(14.0)
Net cash provided by (used in) financing activities	(384.0)	1,450.9	(508.6)
Net increase (decrease) in cash and cash equivalents	(248.8)	154.8	700.9
Cash and cash equivalents at beginning of period	2,719.6	2,564.8	1,863.9
Cash and cash equivalents at end of period	2,470.8	2,719.6	2,564.8
Supplemental information:
Cash paid for interest	148.6	162.0	149.6
Cash paid for income taxes	79.3	178.8	$ 129.6
Supplemental disclosure of non-cash activities:
Assets received in kind for pension risk transfer transactions		$ 594.3
Asset and liability changes resulting from exchange agreement to exit real estate joint ventures:
Real estate properties received	743.2
Long-term debt assumed on real estate properties received	269.0
Increase in other investments due to discontinuing equity method accounting	$ 222.4