Investments (excluding Consolidated Investment Entities) - Mortgage Loans (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Maximum loan to value ratio generally allowed	75.00%
Commercial mortgage loans	$ 8,689,000,000	$ 8,006,000,000
Collective valuation allowance	(3,000,000)	(3,000,000)
Total net commercial mortgage loans	8,686,000,000	8,003,000,000
Impairment of Real Estate	0	0
Impaired
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial mortgage loans	4,000,000	5,000,000
Total net commercial mortgage loans	4,000,000	5,000,000
Non Impaired
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial mortgage loans	8,685,000,000	8,001,000,000
Collective valuation allowance	(3,000,000)	(3,000,000)
Total net commercial mortgage loans	$ 8,682,000,000	$ 7,998,000,000