Investments (Credit Quality of Residential Mortgage Loans) (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Financing Receivable, Recorded Investment [Line Items]
Recorded Investment	$ 14,473	$ 13,652
% of Total	100.00%	100.00%
Performing
Financing Receivable, Recorded Investment [Line Items]
% of Total	98.50%	98.40%
Nonperforming
Financing Receivable, Recorded Investment [Line Items]
% of Total	1.50%	1.60%
Mortgage Loans | Residential
Financing Receivable, Recorded Investment [Line Items]
Recorded Investment	$ 2,661	$ 2,276
Mortgage Loans | Residential | Performing
Financing Receivable, Recorded Investment [Line Items]
Recorded Investment	2,622	2,240
Mortgage Loans | Residential | Nonperforming
Financing Receivable, Recorded Investment [Line Items]
Recorded Investment	$ 39	$ 36