Fair Value Measurements - Instruments not Carried at Fair Value (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended
Jun. 30, 2013	Dec. 31, 2012
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Commercial mortgage loans	$ 2,570	$ 2,851
Percent Unrestricted Contractholder Deposit Funds	60.00%
Estimate Of Fair Value Fair Value Disclosure [Member] \| Fair Value Inputs Level 2 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Long-term debt, including current maturities, excluding capital leases	5,523	5,821
Estimate Of Fair Value Fair Value Disclosure [Member] \| Fair Value Inputs Level 3 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Commercial mortgage loans	2,661	2,999
Contractholder deposit funds, excluding universal life products	1,084	1,082
Carrying Reported Amount Fair Value Disclosure [Member] \| Fair Value Inputs Level 2 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Long-term debt, including current maturities, excluding capital leases	4,989	4,986
Carrying Reported Amount Fair Value Disclosure [Member] \| Fair Value Inputs Level 3 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Commercial mortgage loans	2,570	2,851
Contractholder deposit funds, excluding universal life products	$ 1,070	$ 1,056

Amount before allowance of commercial loans issued to businesses to acquire, develop, construct, improve, or refinance land or building. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes loans covered under loss sharing agreements.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 3

-URI http://asc.fasb.org/extlink&oid=7512638&loc=d3e5066-111524

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

-Publisher AICPA

-Name Statement of Position (SOP)

-Number 01-6

-Paragraph 13

-Subparagraph e

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 60

-Paragraph 47

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 7

-Subparagraph a

-Article 9

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 210.9-03.7(a))

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

Reference 6: 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(c))

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

Reference 7: http://www.xbrl.org/2003/role/presentationRef

-Publisher AICPA

-Name Audit and Accounting Guide (AAG)

-Number AAG-DEP

-Paragraph 51, 52, 53

-IssueDate 2006-05-01

-Chapter 8

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

+ Details