Investments Investments - Other investments by type (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Investment Holdings [Line Items]
Other	$ 1,322	$ 1,254
Agent loans
Investment Holdings [Line Items]
Other	570	538
Bank loans
Investment Holdings [Line Items]
Other	447	437
Real estate
Investment Holdings [Line Items]
Other	212	157
Derivatives and other
Investment Holdings [Line Items]
Other	$ 93	$ 122

Amount of investments classified as other.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.1(f,g))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.12)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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