Derivative Instruments - Gross amounts of derivative fair values contained in the consolidated balance sheet (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015		Dec. 31, 2014
Derivatives, Fair Value [Line Items]
Gross amounts recognized in balance sheet	$ 257,880		$ 136,659
Asset derivative fair value	257,293		135,963
Gross amounts recognized in balance sheet	122,235		31,184
Liability derivative fair value	121,648		30,488
Derivatives designated as hedging instruments
Derivatives, Fair Value [Line Items]
Derivative Asset, Notional Amount	204,811		2,300,609
Gross amounts recognized in balance sheet	38,376	[1]	121,862	[1]
Liability derivative notional amount	204,811		302,211
Gross amounts recognized in balance sheet	26,505	[1]	2,936	[1]
Derivatives designated as hedging instruments | Foreign exchange contracts
Derivatives, Fair Value [Line Items]
Derivative Asset, Notional Amount	204,811		2,300,609
Gross amounts recognized in balance sheet	38,376	[1]	121,862	[1]
Liability derivative notional amount	204,811		302,211
Gross amounts recognized in balance sheet	26,505	[1]	2,936	[1]
Derivatives not designated as hedging instruments
Derivatives, Fair Value [Line Items]
Derivative Asset, Notional Amount	2,770,578		592,791
Gross amounts recognized in balance sheet	219,504	[1]	14,797	[1]
Liability derivative notional amount	7,708,973		5,804,625
Gross amounts recognized in balance sheet	95,730	[1]	28,248	[1]
Derivatives not designated as hedging instruments | Investment related derivatives | Interest rate exposure
Derivatives, Fair Value [Line Items]
Derivative Asset, Notional Amount	264,527		394,597
Gross amounts recognized in balance sheet	224	[1]	206	[1]
Liability derivative notional amount	13,033		20,782
Gross amounts recognized in balance sheet	65	[1]	51	[1]
Derivatives not designated as hedging instruments | Investment related derivatives | Foreign exchange contracts
Derivatives, Fair Value [Line Items]
Derivative Asset, Notional Amount	23,400		7,385
Gross amounts recognized in balance sheet	498	[1]	403	[1]
Liability derivative notional amount	190,368		288,376
Gross amounts recognized in balance sheet	7,709	[1]	4,724	[1]
Derivatives not designated as hedging instruments | Investment related derivatives | Credit exposure
Derivatives, Fair Value [Line Items]
Derivative Asset, Notional Amount	2,408		2,408
Gross amounts recognized in balance sheet	205	[1]	165	[1]
Liability derivative notional amount	14,270		14,270
Gross amounts recognized in balance sheet	9,836	[1]	9,836	[1]
Derivatives not designated as hedging instruments | Investment related derivatives | Financial market exposure
Derivatives, Fair Value [Line Items]
Derivative Asset, Notional Amount	33,362		46,145
Gross amounts recognized in balance sheet	513	[1]	360	[1]
Liability derivative notional amount	33,136		33,670
Gross amounts recognized in balance sheet	63	[1]	34	[1]
Derivatives not designated as hedging instruments | Other non-investment derivatives | Foreign exchange contracts
Derivatives, Fair Value [Line Items]
Derivative Asset, Notional Amount	2,304,633		0
Gross amounts recognized in balance sheet	205,083	[1]	0	[1]
Liability derivative notional amount	2,366,968		0
Gross amounts recognized in balance sheet	65,294	[1]	0	[1]
Derivatives not designated as hedging instruments | Other non-investment derivatives | Other Credit Derivatives [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Notional Amount	31,060		31,060
Gross amounts recognized in balance sheet	218		60
Liability derivative notional amount	0		0
Gross amounts recognized in balance sheet	0		0
Derivatives not designated as hedging instruments | Other non-investment derivatives | Guaranteed minimum income benefit contract
Derivatives, Fair Value [Line Items]
Derivative Asset, Notional Amount	45,658		46,249
Gross amounts recognized in balance sheet	12,763	[1]	13,603	[1]
Liability derivative notional amount	45,658		46,249
Gross amounts recognized in balance sheet	12,763	[1]	13,603	[1]
Derivatives not designated as hedging instruments | Other non-investment derivatives | Modified coinsurance funds withheld contract
Derivatives, Fair Value [Line Items]
Derivative Asset, Notional Amount	65,530	[2]	64,947	[2]
Gross amounts recognized in balance sheet	0	[1],[2]	0	[1],[2]
Liability derivative notional amount	5,045,540	[2]	5,401,278	[2]
Gross amounts recognized in balance sheet	$ 0	[1],[2]	$ 0	[1],[2]

[1] Derivative instruments in an asset or liability position are included within Other assets or Other liabilities, respectively, in the balance sheets on a net basis where the Company has both a legal right of offset and the intention to settle the contracts on a net basis.

[2] The fair value movements in derivative assets and liabilities relating to modified coinsurance funds withheld contracts are included within the associated asset or liability at each period end on the face of the balance sheets. Notional amounts associated with reinsurance agreements under which the Company assumes reinsurance risk are recorded as asset derivative notional amounts. Notional amounts associated with the Life Retro Arrangements under which the Company cedes reinsurance risk are recorded as liability derivative notional amounts. Included in the liability derivative notional amount as of March 31, 2015 is the cumulative net realized and unrealized loss on life retrocession embedded derivative of $654.6 million