Variable Interest Entities (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014
Variable Interest Entity [Line Items]
Methodology for determining whether the Company is primary beneficiary	When the Company becomes involved with a variable interest entity and when the nature of the Company’s involvement with the entity changes, to determine if the Company is the primary beneficiary and must consolidate the entity, it evaluates: the structure and purpose of the entity; the risks and rewards created by and shared through the entity; and the entity’s participants’ ability to direct its activities, receive its benefits and absorb its losses. Participants include the entity’s sponsors, equity holders, guarantors, creditors and servicers.
Investment Entities [Member]
Variable Interest Entity [Line Items]
Nature and extent of involvement with variable interest entity	In the normal course of its investing activities, the Company makes passive investments in securities that are issued by variable interest entities for which the Company is not the sponsor or manager. These investments are predominantly asset-backed securities primarily collateralized by foreign bank obligations or mortgage-backed securities. The asset-backed securities are largely fixed-rate debt securities issued by trusts that hold perpetual floating-rate subordinated notes issued by foreign banks. The mortgage-backed securities are senior interests in pools of commercial or residential mortgages created and held by special-purpose entities to provide investors with diversified exposure to these assets. The Company owns senior securities issued by several entities and receives fixed-rate cash flows from the underlying assets in the pools.
Maximum exposure to loss related to arrangements with variable interest entity	762
Significant sources of exposure related to arrangement with variable interest entity	The Company’s maximum potential exposure to loss related to the investment entities is limited to the aggregate carrying amount of its investments of $762 million as of December 31, 2014 reported in fixed maturities and equity securities; the Company’s combined ownership interests are insignificant relative to the total principal amounts issued by these entities.
Independent Physician Associations [Member]
Variable Interest Entity [Line Items]
Nature and extent of involvement with variable interest entity	To provide certain services to its Medicare Advantage customers, the Company contracts with independent physician associations (“IPAs”) that are variable interest entities. Physicians provide health care services to the Medicare Advantage customers and the Company provides medical management and administrative services to the IPAs.
Maximum exposure to loss related to arrangements with variable interest entity
Significant sources of exposure related to arrangement with variable interest entity	The Company’s maximum exposure to loss related to the IPA arrangements is limited to the liability for incurred but not reported claims for the Company’s Medicare Advantage customers. These liabilities are not material and are generally secured by deposits maintained by the IPAs.