Dispositions - Separation of Brighthouse - Ongoing Transactions (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Jul. 21, 2017	Jun. 30, 2017	Apr. 30, 2017
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Discontinued Operation, Intra-Entity Amounts, Discontinued Operation after Disposal, Revenue	$ 48
Brighthouse Financial, Inc [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Revenue from Related Parties	57
Line of Credit Facility, Maximum Borrowing Capacity		$ 600	$ 536	$ 3,000
Committed Credit Facility Six [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	2,896
Letters of Credit Outstanding, Amount	2,354
Committed Credit Facility Six [Member] | Brighthouse Financial, Inc [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	2,900
Letters of Credit Outstanding, Amount	$ 2,400