Investments (Schedule of Fixed Maturity and Equity Securities) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Investment Holdings [Line Items]
Held for investment, amortized cost	$ 76,432us-gaap_HeldToMaturitySecurities	$ 76,255us-gaap_HeldToMaturitySecurities
Held for investment, fair value	75,838	60,840
Fixed Maturity Securities [Member] \| Available For Sale [Member]
Investment Holdings [Line Items]
Available for sale securities, amortized cost	30,205,046	26,527,730
Available for sale securities, gross unrealized gains	2,395,577	928,699
Available for sale securities, gross unrealized losses	(155,421)	(845,982)
Available for sale securities, fair value	32,445,202	26,610,447
Equity Securities [Member] \| Available For Sale [Member]
Investment Holdings [Line Items]
Available for sale securities, amortized cost	7,509	7,503
Available for sale securities, gross unrealized gains	296	275
Available for sale securities, gross unrealized losses	0	0
Available for sale securities, fair value	7,805	7,778
United States Government Full Faith and Credit [Member] \| Fixed Maturity Securities [Member] \| Available For Sale [Member]
Investment Holdings [Line Items]
Available for sale securities, amortized cost	137,710	44,852
Available for sale securities, gross unrealized gains	765	367
Available for sale securities, gross unrealized losses	(15)	(2,294)
Available for sale securities, fair value	138,460	42,925
United States Government Sponsored Agencies [Member] \| Fixed Maturity Securities [Member] \| Available For Sale [Member]
Investment Holdings [Line Items]
Available for sale securities, amortized cost	1,364,424	1,313,776
Available for sale securities, gross unrealized gains	43,399	1,875
Available for sale securities, gross unrealized losses	(13,933)	(121,362)
Available for sale securities, fair value	1,393,890	1,194,289
United States Municipalities, States and Territories [Member] \| Fixed Maturity Securities [Member] \| Available For Sale [Member]
Investment Holdings [Line Items]
Available for sale securities, amortized cost	3,293,551	3,181,032
Available for sale securities, gross unrealized gains	430,469	164,785
Available for sale securities, gross unrealized losses	(711)	(39,074)
Available for sale securities, fair value	3,723,309	3,306,743
Foreign Government Obligations [Member] \| Fixed Maturity Securities [Member] \| Available For Sale [Member]
Investment Holdings [Line Items]
Available for sale securities, amortized cost	181,128	86,112
Available for sale securities, gross unrealized gains	16,628	8,907
Available for sale securities, gross unrealized losses	(3,953)	(3,462)
Available for sale securities, fair value	193,803	91,557
Corporate Securities [Member] \| Fixed Maturity Securities [Member] \| Available For Sale [Member]
Investment Holdings [Line Items]
Available for sale securities, amortized cost	19,984,747	17,142,118
Available for sale securities, gross unrealized gains	1,628,941	606,948
Available for sale securities, gross unrealized losses	(123,396)	(516,029)
Available for sale securities, fair value	21,490,292	17,233,037
Corporate Securities [Member] \| Fixed Maturity Securities [Member] \| Held For Investment [Member]
Investment Holdings [Line Items]
Held for investment, amortized cost	76,432	76,255
Held for investment, gross unrealized gains	0	0
Held for investment, gross unrealized losses	(594)	(15,415)
Held for investment, fair value	75,838	60,840
Residential Mortgage Backed Securities [Member] \| Fixed Maturity Securities [Member] \| Available For Sale [Member]
Investment Holdings [Line Items]
Available for sale securities, amortized cost	1,616,846	1,895,913
Available for sale securities, gross unrealized gains	136,704	119,230
Available for sale securities, gross unrealized losses	(2,205)	(43,183)
Available for sale securities, fair value	1,751,345	1,971,960
Commercial Mortgage Backed Securities [Member] \| Fixed Maturity Securities [Member] \| Available For Sale [Member]
Investment Holdings [Line Items]
Available for sale securities, amortized cost	2,720,294	1,821,988
Available for sale securities, gross unrealized gains	90,649	3,287
Available for sale securities, gross unrealized losses	(3,323)	(89,815)
Available for sale securities, fair value	2,807,620	1,735,460
Other Asset Backed Securities [Member] \| Fixed Maturity Securities [Member] \| Available For Sale [Member]
Investment Holdings [Line Items]
Available for sale securities, amortized cost	906,346	1,041,939
Available for sale securities, gross unrealized gains	48,022	23,300
Available for sale securities, gross unrealized losses	(7,885)	(30,763)
Available for sale securities, fair value	$ 946,483	$ 1,034,476

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 25

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=28360136&loc=d3e22054-111558

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 5

-Subparagraph (aa)

-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27232-111563

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 45

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6871852&loc=d3e26610-111562

+ Details

Name:	us-gaap_AvailableForSaleSecurities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27161-111563

+ Details

Name:	us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27161-111563

+ Details

Name:	us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.2)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_AvailableForSaleSecuritiesAmortizedCost
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount after other than temporary impairment (OTTI) accretion, of investments in debt securities classified as held-to-maturity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 5

-Subparagraph (f)

-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27232-111563

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 25

-Paragraph 1

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=28360136&loc=d3e22054-111558

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 5

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27232-111563

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-03.1)

-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-03.6)

-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

+ Details

Name:	us-gaap_HeldToMaturitySecurities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of accumulated unrealized gain on investments in debt securities classified as held-to-maturity.

+ References

+ Details

Name:	us-gaap_HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingGain
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of accumulated unrealized loss on investments in debt securities classified as held-to-maturity.

+ References

+ Details

Name:	us-gaap_HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Fair value of investments in debt securities classified as held-to-maturity.

+ References

+ Details

Name:	us-gaap_HeldToMaturitySecuritiesFairValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	us-gaap_InvestmentHoldingsLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_DebtSecurityAxis=us-gaap_AssetBackedSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtSecurityAxis=us-gaap_CommercialMortgageBackedSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtSecurityAxis=us-gaap_CorporateDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtSecurityAxis=us-gaap_ForeignGovernmentDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtSecurityAxis=us-gaap_ResidentialMortgageBackedSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtSecurityAxis=us-gaap_USGovernmentCorporationsAndAgenciesSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtSecurityAxis=us-gaap_USStatesAndPoliticalSubdivisionsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtSecurityAxis=us-gaap_USTreasurySecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_EquitySecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_FixedMaturitiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: