Fair value measurements Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation (Details) - USD ($) $ in Millions		3 Months Ended				6 Months Ended
		Jun. 30, 2017		Jun. 30, 2016		Jun. 30, 2017		Jun. 30, 2016		Mar. 31, 2017	Dec. 31, 2016	Mar. 31, 2016	Dec. 31, 2015
Guaranteed Minimum Income Benefit [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Reported liabilities		$ 684		$ 1,300		$ 684		$ 1,300		$ 774	$ 853	$ 1,100	$ 888
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance - Beginning of Period, Liabilities		466	[1]	839	[2]	559	[1]	609	[1],[2]
Transfers into level 3, liability		9		0		9		0
Transfers out of Level 3, Liabilities		0				0		0
Change in Net Unrealized Gains (Losses) included in OCI, Liabilities		0		0		0		0
Net Realized Gains/Losses, Liabilities		(118)		132	[2]	(211)		362	[2]
Purchases, Liabilities		0		0		0		0
Sales, Liabilities		0		0		0		0
Settlements, Liabilities		0		0		0		0
Balance - End of Period, Liabilities	[1]	357		971	[2]	357		971	[2]
Fair Value, Liabilities Measured on Recurring Basis, Change in Unrealized Gain (Loss)		(118)		132		(211)		362
Other Derivative Instruments Fair Value [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance - Beginning of Period, Liabilities		11		10		13		6
Transfers into level 3, liability		0		0		0		0
Transfers out of Level 3, Liabilities		(9)				(9)		0
Change in Net Unrealized Gains (Losses) included in OCI, Liabilities		0		0		0		0
Net Realized Gains/Losses, Liabilities		0		0		(2)		2
Purchases, Liabilities		0		0		0		2
Sales, Liabilities		0		0		0		0
Settlements, Liabilities		0		0		0		0
Balance - End of Period, Liabilities		2		10		2		10
Fair Value, Liabilities Measured on Recurring Basis, Change in Unrealized Gain (Loss)		$ 0		$ 0		$ (2)		$ 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 $684 million at June 30, 2017, and $774 million at March 31, 2017, which includes a fair value derivative adjustment of $357 million and $466 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 $1.3 billion at June 30, 2016, and $1.1 billion at March 31, 2016, which includes a fair value derivative adjustment of $971 million and $839 million, respectively. Assets Liabilities Six Months EndedAvailable-for-Sale Debt SecuritiesEquitysecuritiesShort-term investmentsOtherinvestments OtherderivativeinstrumentsGLB(1)June 30, 2017Foreign Corporatesecurities MBS (in millions of U.S. dollars) Balance – beginning of period$74 $681 $45 $41$25$225 $13$559Transfers into Level 3— 57 — ——— —9Transfers out of Level 3— (67) — ——— (9)—Change in Net Unrealized Gains (Losses) included in OCI2 (8) — 1—3 ——Net Realized Gains/Losses1 (1) — ——— (2)(211)Purchases33 221 1 61424 ——Sales(22) (55) (1) (9)—— ——Settlements(3) (81) — —(32)(9) ——Balance – end of period$85 $747 $45 $39$7$243 $2$357Net Realized Gains/Losses Attributable to Changes in Fair Value at the Balance Sheet Date$— $— $— $—$—$— $(2)$(211)(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 $684 million at June 30, 2017, and $853 million at December 31, 2016, which includes a fair value derivative adjustment of $357 million and $559 million, respectively. Assets LiabilitiesSix Months EndedAvailable-for-Sale Debt Securities Equitysecurities Short-term investments Otherinvestments Other derivative instruments GLB(1)June 30, 2016Foreign Corporatesecurities MBS (in millions of U.S. dollars) Balance – beginning of period$57 $174 $53 $16 $— $212 $6 $609Transfers into Level 39 18 — — — — — —Transfers out of Level 3(2) — — — — — — —Change in Net Unrealized Gains (Losses) included in OCI9 11 — (1) — — — —Net Realized Gains/Losses(6) (8) — 1 — — 2 362Purchases (2)32 124 1 23 50 14 2 —Sales(8) (30) (5) (2) — — — —Settlements(4) (8) — — — (10) — —Balance – end of period$87 $281 $49 $37 $50 $216 $10 $971Net Realized Gains/Losses Attributable to Changes in Fair Value at the Balance Sheet Date$(5) $(7) $— $— $— $— $2 $362(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 $1.3 billion at June 30, 2016, and $888 million at December 31, 2015, which includes a fair value derivative adjustment of $971 million and $609 million, respectively.(2) Includes acquired invested assets as a result of the Chubb Corp acquisition.