Investments - Mortgage Loans (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	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	$ 4,919,000,000	$ 4,911,000,000
Collective valuation allowance	(1,000,000)	(1,000,000)
Total net commercial mortgage loans	4,918,000,000	4,910,000,000
Impairments on mortgage loans	0	0	$ 0
Impaired
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial mortgage loans	4,000,000	4,000,000
Total net commercial mortgage loans	4,000,000	4,000,000
Not Impaired
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial mortgage loans	4,915,000,000	4,907,000,000
Collective valuation allowance	(1,000,000)	(1,000,000)
Total net commercial mortgage loans	$ 4,914,000,000	$ 4,906,000,000