Fair value measurements Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018		Mar. 31, 2017		Dec. 31, 2017	Mar. 31, 2016
Guaranteed Minimum Income Benefit [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Reported liabilities	$ 529		$ 774		$ 550	$ 853
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance - Beginning of Period, Liabilities	204	[1]	559	[2]
Transfers into level 3, liability	0		0
Transfers out of Level 3, Liabilities	0		0
Change in Net Unrealized Gains (Losses) included in OCI, Liabilities	0		0
Net Realized Gains/Losses, Liabilities	(37)		(93)
Purchases, Liabilities	0		0
Sales, Liabilities	0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Settlements	0		0
Balance - End of Period, Liabilities	167	[1]	466	[2]
Fair Value, Liabilities Measured on Recurring Basis, Change in Unrealized Gain (Loss)	(37)		(93)
Other Derivative Instruments Fair Value [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance - Beginning of Period, Liabilities	2		13
Transfers into level 3, liability	0		0
Transfers out of Level 3, Liabilities	0		0
Change in Net Unrealized Gains (Losses) included in OCI, Liabilities	0		0
Net Realized Gains/Losses, Liabilities	0		(2)
Purchases, Liabilities	0		0
Sales, Liabilities	0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Settlements	0		0
Balance - End of Period, Liabilities	2		11
Fair Value, Liabilities Measured on Recurring Basis, Change in Unrealized Gain (Loss)	$ 0		$ (2)

[1] Our GLB reinsurance product meets the definition of a derivative instrument for accounting purposes and is accordingly carried at fair value. Excluded from the table above is the portion of the GLB derivative liability classified as Future policy benefits in the Consolidated balance sheets. The liability for GLB reinsurance was $529 million at March 31, 2018, and $550 million at December 31, 2017, which includes a fair value derivative adjustment of $167 million and $204 million, respectively.

[2] Our GLB reinsurance product meets the definition of a derivative instrument for accounting purposes and is accordingly carried at fair value. Excluded from the table above is the portion of the GLB derivative liability classified as Future policy benefits in the Consolidated balance sheets. The liability for GLB reinsurance was $774 million at March 31, 2017, and $853 million at December 31, 2016, which includes a fair value derivative adjustment of $466 million and $559 million, respectively.