Equity (Schedule of Reclassifications out of AOCI) (Details) - USD ($) $ in Thousands		3 Months Ended				9 Months Ended
		Sep. 30, 2017		Sep. 30, 2016		Sep. 30, 2017		Sep. 30, 2016
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Investment related gains (losses), net		$ 23,043		$ 86,624		$ 160,451		$ 118,665
Investment income		556,918		489,727		1,589,820		1,414,659
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest		340,162		287,600		887,321		748,403
Income Tax Expense (Benefit)		(112,571)		(88,881)		(282,028)		(237,109)
Net income		227,591		198,719		605,293		511,294
Unrealized Appreciation Depreciation Of Investments [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest		12,085		84,778		51,407		109,145
Income Tax Expense (Benefit)		(3,991)		(27,680)		(16,015)		(32,676)
Net income		8,094		57,098		35,392		76,469
Unrealized Appreciation Depreciation Of Investments [Member] | Unrealized Gains Losses On Available For Sale Securities [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Investment related gains (losses), net		10,515		72,351		39,032		84,250
Unrealized Appreciation Depreciation Of Investments [Member] | Interest Rate Swap [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	[1]	230		200		560		454
Unrealized Appreciation Depreciation Of Investments [Member] | Forward Contracts [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	[1]	224		137		286		(120)
Unrealized Appreciation Depreciation Of Investments [Member] | DAC Attributed To Unrealized Gains Losses [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Deferred policy acquisition costs attributed to unrealized gains and losses		1,116	[1]	12,090	[1]	(11,529)	[2]	24,561	[2]
Amortization Of Unrealized Pension And Postretirement Benefits [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest		(1,071)		(786)		(4,006)		(4,253)
Income Tax Expense (Benefit)		375		276		1,402		1,489
Net income		(696)		(510)		(2,604)		(2,764)
Amounts Reclassified From AOCI [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Net income		7,398		56,588		32,788		73,705
Prior Service Cost [Member] | Amortization Of Unrealized Pension And Postretirement Benefits [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Prior service cost		590	[2]	391	[2]	732	[3]	238	[3]
Actuarial Gains Losses [Member] | Amortization Of Unrealized Pension And Postretirement Benefits [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Actuarial gains/(losses)		$ (1,661)	[2]	$ (1,177)	[2]	$ 4,738	[3]	$ (4,491)	[3]

[1] See Note 5 - “Derivative Instruments” for additional information on cash flow hedges.

[2] This AOCI component is included in the computation of the deferred policy acquisition cost. See Note 8 – “Deferred Policy Acquisition Costs” of the 2016 Annual Report for additional details.

[3] This AOCI component is included in the computation of the net periodic pension cost. See Note 10 – “Employee Benefit Plans” for additional details.