Debt Instrument, Number of Subsidiaries, one hundred percent of common stock as collateral

No definition available.

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- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

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- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
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- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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- Definition

Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

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- Definition

Represents the charge against earnings during the period for commitment fees and debt issuance expenses.

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- Definition

The cash outflow from the repayment of long-term borrowing where a lender is placed in a lien position behind debt having a higher priority of repayment (senior) in case of liquidation of the entity's assets before its maturity.

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- Definition

Aggregate net gain (loss) on all derivative instruments recognized in earnings during the period, before tax effects.

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- Definition

Difference between the fair value of payments made and the carrying amount of debt which is extinguished prior to maturity.

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-Publisher FASB
-Name Accounting Standards Codification
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- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

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-Publisher FASB
-Name Accounting Standards Codification
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- Definition

Amount of long-term debt payable, sinking fund requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing in the next fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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- Definition

The cash inflow from additional borrowings, net of cash paid to third parties in connection with debt origination.

+ References

No definition available.

+ Details

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- Definition

Amount of cash inflow from contractual arrangement with the lender, including but not limited to, letter of credit, standby letter of credit and revolving credit arrangements.

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-Publisher FASB
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- Definition

The cash outflow during the period from the repayment of aggregate short-term and long-term debt. Excludes payment of capital lease obligations.

+ References

No definition available.

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Debt - Additional Information (Detail)	1 Months Ended		9 Months Ended	12 Months Ended
Debt - Additional Information (Detail)	Apr. 30, 2017 USD ($)	Aug. 31, 2016 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2017 USD ($)	Mar. 31, 2017	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Debt Instrument [Line Items]
Early Repayment of Subordinated Debt				$ 635,600,000		$ 18,200,000	$ 19,300,000
Gain (Loss) on Derivative Instruments, Net, Pretax				0		(20,000,000)	(20,700,000)
Debt Instrument, Periodic Payment, Principal in Next Twelve Months			$ 25,000,000	$ 25,000,000
Debt Instrument, Number of Subsidiaries, one hundred percent of common stock as collateral			3	3
Discretionary Line of Credit
Debt Instrument [Line Items]
Debt Instrument, Term				30 days
Line of Credit Facility, Maximum Borrowing Capacity			$ 250,000,000	$ 250,000,000
Proceeds from Lines of Credit				0		0
Discretionary Line of Credit \| Federal Funds Rate
Debt Instrument [Line Items]
Basis points			0.50%		0.50%
Terminated Discretionary Line of Credit [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 100,000,000
4.125% Senior Notes due 2047
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 850,000,000		$ 850,000,000	$ 850,000,000		0
Debt Instrument, Interest Rate, Stated Percentage	4.125%		4.125%	4.125%
Proceeds from Debt, Net of Issuance Costs	$ 841,100,000
Debt Related Commitment Fees and Debt Issuance Costs	$ 1,500,000
2.45% Senior Notes Due 2027
Debt Instrument [Line Items]
Debt Instrument, Face Amount		$ 500,000,000	$ 500,000,000	$ 500,000,000		500,000,000
Debt Instrument, Interest Rate, Stated Percentage		2.45%	2.45%	2.45%
Proceeds from Debt, Net of Issuance Costs		$ 495,600,000
Debt Related Commitment Fees and Debt Issuance Costs		900,000
6.70% Fixed-to-Floating Rate Junior Subordinated Debentures due 2067
Debt Instrument [Line Items]
Debt Instrument, Face Amount			$ 0	$ 0		1,000,000,000
Debt Instrument, Interest Rate, Stated Percentage			6.70%	6.70%
Early Repayment of Subordinated Debt				$ 30,900,000		19,800,000
Gains (losses) on extinguishment of debt				200,000		1,600,000
Trust Preferred Debt Securities and Senior Notes [Member] \| Other Debt Instruments [Member]
Debt Instrument [Line Items]
Repayments of Debt				$ 65,200,000
Loans Payable [Member] \| Fixed Rate, Five Year Loan [Member]
Debt Instrument [Line Items]
Debt Instrument, Term				5 years
London Interbank Offered Rate (LIBOR) [Member] \| Notes Payable, Other Payables [Member] \| Other Debt Instruments [Member]
Debt Instrument [Line Items]
Basis points				2.25%
Designated as Hedging Instrument [Member] \| Ineffective Cash Flow Hedge [Member]
Debt Instrument [Line Items]
Gain (Loss) on Derivative Instruments, Net, Pretax				$ 0		$ (1,300,000)	$ 200,000
Designated as Hedging Instrument [Member] \| Ineffective Cash Flow Hedge [Member] \| 2.45% Senior Notes Due 2027
Debt Instrument [Line Items]
Gain (Loss) on Derivative Instruments, Net, Pretax		$ (1,400,000)		(1,400,000)
debt extinguishment [Member] \| 6.70% Fixed-to-Floating Rate Junior Subordinated Debentures due 2067
Debt Instrument [Line Items]
Early Repayment of Subordinated Debt				$ 563,700,000