Investments (Credit Quality of Commercial Mortgage Loans) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Receivable, Gross, Commercial, Mortgage	$ 48,463	$ 44,375
Loans Receivable Commercial Mortgage Percentage	100.00%	100.00%
Estimated Fair Value Commercial Mortgage	$ 48,747	$ 45,084
Estimated Fair Value Commercial Mortgage Percentage	100.00%	100.00%
Mortgage Loans By Credit Quality Indicator Range One [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Receivable, Gross, Commercial, Mortgage	$ 41,288	$ 38,757
Loans Receivable Commercial Mortgage Percentage	85.20%	87.40%
Estimated Fair Value Commercial Mortgage	$ 41,599	$ 39,528
Estimated Fair Value Commercial Mortgage Percentage	85.30%	87.70%
Mortgage Loans By Credit Quality Indicator Range Two [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Receivable, Gross, Commercial, Mortgage	$ 5,815	$ 4,400
Loans Receivable Commercial Mortgage Percentage	12.00%	9.90%
Estimated Fair Value Commercial Mortgage	$ 5,849	$ 4,408
Estimated Fair Value Commercial Mortgage Percentage	12.00%	9.80%
Mortgage Loans By Credit Quality Indicator Range Three [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Receivable, Gross, Commercial, Mortgage	$ 688	$ 502
Loans Receivable Commercial Mortgage Percentage	1.40%	1.10%
Estimated Fair Value Commercial Mortgage	$ 664	$ 476
Estimated Fair Value Commercial Mortgage Percentage	1.40%	1.00%
Mortgage Loans By Credit Quality Indicator Range Four [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Receivable, Gross, Commercial, Mortgage	$ 672	$ 716
Loans Receivable Commercial Mortgage Percentage	1.40%	1.60%
Estimated Fair Value Commercial Mortgage	$ 635	$ 672
Estimated Fair Value Commercial Mortgage Percentage	1.30%	1.50%
Debt Service Coverage Ratio Range One [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Receivable, Gross, Commercial, Mortgage	$ 47,069	$ 41,892
Debt Service Coverage Ratio Range One [Member] | Mortgage Loans By Credit Quality Indicator Range One [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Receivable, Gross, Commercial, Mortgage	40,360	37,073
Debt Service Coverage Ratio Range One [Member] | Mortgage Loans By Credit Quality Indicator Range Two [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Receivable, Gross, Commercial, Mortgage	5,790	4,183
Debt Service Coverage Ratio Range One [Member] | Mortgage Loans By Credit Quality Indicator Range Three [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Receivable, Gross, Commercial, Mortgage	423	235
Debt Service Coverage Ratio Range One [Member] | Mortgage Loans By Credit Quality Indicator Range Four [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Receivable, Gross, Commercial, Mortgage	496	401
Debt Service Coverage Ratio Range Two [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Receivable, Gross, Commercial, Mortgage	1,212	1,959
Debt Service Coverage Ratio Range Two [Member] | Mortgage Loans By Credit Quality Indicator Range One [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Receivable, Gross, Commercial, Mortgage	827	1,483
Debt Service Coverage Ratio Range Two [Member] | Mortgage Loans By Credit Quality Indicator Range Two [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Receivable, Gross, Commercial, Mortgage	0	98
Debt Service Coverage Ratio Range Two [Member] | Mortgage Loans By Credit Quality Indicator Range Three [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Receivable, Gross, Commercial, Mortgage	209	210
Debt Service Coverage Ratio Range Two [Member] | Mortgage Loans By Credit Quality Indicator Range Four [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Receivable, Gross, Commercial, Mortgage	176	168
Debt Service Coverage Ratio Range Three [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Receivable, Gross, Commercial, Mortgage	182	524
Debt Service Coverage Ratio Range Three [Member] | Mortgage Loans By Credit Quality Indicator Range One [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Receivable, Gross, Commercial, Mortgage	101	201
Debt Service Coverage Ratio Range Three [Member] | Mortgage Loans By Credit Quality Indicator Range Two [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Receivable, Gross, Commercial, Mortgage	25	119
Debt Service Coverage Ratio Range Three [Member] | Mortgage Loans By Credit Quality Indicator Range Three [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Receivable, Gross, Commercial, Mortgage	56	57
Debt Service Coverage Ratio Range Three [Member] | Mortgage Loans By Credit Quality Indicator Range Four [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Receivable, Gross, Commercial, Mortgage	$ 0	$ 147