Consolidated Statements of Changes in Partnership Capital Subject to Mandatory Redemption - USD ($) $ in Millions	Total	Limited Partnership Capital [Member]	Subordinated Limited Partnership Capital [Member]	General Partnership Capital [Member]
TOTAL PARTNERSHIP CAPITAL SUBJECT TO MANDATORY REDEMPTION at Dec. 31, 2014	$ 2,218	$ 684	$ 362	$ 1,172
Reserve for anticipated withdrawals at Dec. 31, 2014	(245)	(52)	(27)	(166)
Partnership capital subject to mandatory redemption, net of reserve for anticipated withdrawals at Dec. 31, 2014	1,973	632	335	1,006
Partnership loans outstanding at beginning of year at Dec. 31, 2014	198	0	1	197
Total partnership capital, including capital financed with partnership loans, net of reserve for anticipated withdrawals at Dec. 31, 2014	2,171	632	336	1,203
Issuance of partnership interests	471	296	43	132
Redemption of partnership interests	(161)	(12)	(9)	(140)
Income allocated to partners	838	121	93	624
Distributions	(491)	(47)	(67)	(377)
Total partnership capital, including capital financed with partnership loans at Dec. 31, 2015	2,828	990	396	1,442
Partnership loans outstanding, reduction to arrive at Partnership Capital at Dec. 31, 2015	(218)	0	(2)	(216)
TOTAL PARTNERSHIP CAPITAL SUBJECT TO MANDATORY REDEMPTION at Dec. 31, 2015	2,610	990	394	1,226
Reserve for anticipated withdrawals at Dec. 31, 2015	(262)	(74)	(26)	(162)
Partnership capital subject to mandatory redemption, net of reserve for anticipated withdrawals at Dec. 31, 2015	2,348	916	368	1,064
Partnership loans outstanding at end of year at Dec. 31, 2015	218	0	2	216
Total partnership capital, including capital financed with partnership loans, net of reserve for anticipated withdrawals at Dec. 31, 2015	2,566	916	370	1,280
Issuance of partnership interests	218	1	61	156
Redemption of partnership interests	(178)	(15)	(5)	(158)
Income allocated to partners	746	100	90	556
Distributions	(452)	(43)	(66)	(343)
Total partnership capital, including capital financed with partnership loans at Dec. 31, 2016	2,900	959	450	1,491
Partnership loans outstanding, reduction to arrive at Partnership Capital at Dec. 31, 2016	(266)	0	(5)	(261)
TOTAL PARTNERSHIP CAPITAL SUBJECT TO MANDATORY REDEMPTION at Dec. 31, 2016	2,634	959	445	1,230
Reserve for anticipated withdrawals at Dec. 31, 2016	(217)	(57)	(24)	(136)
Partnership capital subject to mandatory redemption, net of reserve for anticipated withdrawals at Dec. 31, 2016	2,417	902	421	1,094
Partnership loans outstanding at end of year at Dec. 31, 2016	266	0	5	261
Total partnership capital, including capital financed with partnership loans, net of reserve for anticipated withdrawals at Dec. 31, 2016	2,683	902	426	1,355
Issuance of partnership interests	222	1	60	161
Redemption of partnership interests	(193)	(13)	(20)	(160)
Income allocated to partners	872	109	109	654
Distributions	(492)	(43)	(73)	(376)
Total partnership capital, including capital financed with partnership loans at Dec. 31, 2017	3,092	956	502	1,634
Partnership loans outstanding, reduction to arrive at Partnership Capital at Dec. 31, 2017	(297)	0	(3)	(294)
TOTAL PARTNERSHIP CAPITAL SUBJECT TO MANDATORY REDEMPTION at Dec. 31, 2017	2,795	956	499	1,340
Reserve for anticipated withdrawals at Dec. 31, 2017	(290)	(66)	(36)	(188)
Partnership capital subject to mandatory redemption, net of reserve for anticipated withdrawals at Dec. 31, 2017	2,505	$ 890	$ 463	$ 1,152
Partnership loans outstanding at end of year at Dec. 31, 2017	$ 297