Investments (Mortgage Loans by Portfolio Segment) (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Loans, Gross	$ 79,091	$ 75,795
Percentage Of Mortgage Loans Held For Investment To Mortgage Loans On Real Estate Commercial And Consumer Net	100.10%	100.10%
Allowance for Loan and Lease Losses, Real Estate	$ 350	$ 342	$ 336	$ 314
Percentage Of Allowance For Loan And Lease Losses Real Estate To Mortgage Loans On Real Estate Commercial And Consumer Net	(0.40%)	(0.50%)
Loans and Leases Receivable, Net Amount	$ 78,741	$ 75,453
Percentage Of Mortgage Loans Held For Investment Net To Mortgage Loans On Real Estate Commercial And Consumer Net	99.70%	99.60%
Mortgage Loans on Real Estate, Commercial and Consumer, Net	$ 78,959	$ 75,752
Percentage Of Loans And Leases Receivable Consumer Other To Mortgage Loans On Real Estate Commercial And Consumer Net	0.30%	0.40%
Percentage Of Mortgage Loans On Real Estate To Mortgage Loans On Real Estate Commercial And Consumer Net	100.00%	100.00%
Residential mortgage loans - FVO
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Loans on Real Estate, Commercial and Consumer, Net	$ 218	$ 299
Agricultural Mortgage Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Loans, Gross	$ 15,752	$ 14,905
Percentage Of Mortgage Loans, Gross	19.90%	19.70%
Allowance for Loan and Lease Losses, Real Estate	$ 48	$ 46	42	41
Commercial Mortgage Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Loans, Gross	$ 49,898	$ 48,463
Percentage Of Mortgage Loans, Gross	63.20%	64.00%
Allowance for Loan and Lease Losses, Real Estate	$ 245	$ 238	232	214
Residential Mortgage Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Loans, Gross	$ 13,441	$ 12,427
Percentage Of Mortgage Loans, Gross	17.00%	16.40%
Allowance for Loan and Lease Losses, Real Estate	$ 57	$ 58	$ 62	$ 59